1309574SglebiusTheory and pragmatics of the tz code and data
2309574Sglebius
3309574Sglebius
4309574Sglebius----- Outline -----
5309574Sglebius
6309574Sglebius	Scope of the tz database
7309574Sglebius	Names of time zone rules
8309574Sglebius	Time zone abbreviations
9309574Sglebius	Accuracy of the tz database
10309574Sglebius	Time and date functions
11309574Sglebius	Calendrical issues
12309574Sglebius	Time and time zones on Mars
13309574Sglebius
14309574Sglebius
15309574Sglebius----- Scope of the tz database -----
16309574Sglebius
17309574SglebiusThe tz database attempts to record the history and predicted future of
18309574Sglebiusall computer-based clocks that track civil time.  To represent this
19309574Sglebiusdata, the world is partitioned into regions whose clocks all agree
20309574Sglebiusabout time stamps that occur after the somewhat-arbitrary cutoff point
21309574Sglebiusof the POSIX Epoch (1970-01-01 00:00:00 UTC).  For each such region,
22309574Sglebiusthe database records all known clock transitions, and labels the region
23309574Sglebiuswith a notable location.  Although 1970 is a somewhat-arbitrary
24309574Sglebiuscutoff, there are significant challenges to moving the cutoff earlier
25309574Sglebiuseven by a decade or two, due to the wide variety of local practices
26309574Sglebiusbefore computer timekeeping became prevalent.
27309574Sglebius
28309574SglebiusClock transitions before 1970 are recorded for each such location,
29309574Sglebiusbecause most systems support time stamps before 1970 and could
30309574Sglebiusmisbehave if data entries were omitted for pre-1970 transitions.
31309574SglebiusHowever, the database is not designed for and does not suffice for
32309574Sglebiusapplications requiring accurate handling of all past times everywhere,
33309574Sglebiusas it would take far too much effort and guesswork to record all
34309574Sglebiusdetails of pre-1970 civil timekeeping.
35309574Sglebius
36309574SglebiusAs described below, reference source code for using the tz database is
37309574Sglebiusalso available.  The tz code is upwards compatible with POSIX, an
38309574Sglebiusinternational standard for UNIX-like systems.  As of this writing, the
39309574Sglebiuscurrent edition of POSIX is:
40309574Sglebius
41309574Sglebius  The Open Group Base Specifications Issue 7
42309574Sglebius  IEEE Std 1003.1, 2013 Edition
43309574Sglebius  <http://pubs.opengroup.org/onlinepubs/9699919799/>
44309574Sglebius
45309574Sglebius
46309574Sglebius
47309574Sglebius----- Names of time zone rules -----
48309574Sglebius
49309574SglebiusEach of the database's time zone rules has a unique name.
50309574SglebiusInexperienced users are not expected to select these names unaided.
51309574SglebiusDistributors should provide documentation and/or a simple selection
52309574Sglebiusinterface that explains the names; for one example, see the 'tzselect'
53309574Sglebiusprogram in the tz code.  The Unicode Common Locale Data Repository
54309574Sglebius<http://cldr.unicode.org/> contains data that may be useful for other
55309574Sglebiusselection interfaces.
56309574Sglebius
57309574SglebiusThe time zone rule naming conventions attempt to strike a balance
58309574Sglebiusamong the following goals:
59309574Sglebius
60309574Sglebius * Uniquely identify every region where clocks have agreed since 1970.
61309574Sglebius   This is essential for the intended use: static clocks keeping local
62309574Sglebius   civil time.
63309574Sglebius
64309574Sglebius * Indicate to experts where that region is.
65309574Sglebius
66309574Sglebius * Be robust in the presence of political changes.  For example, names
67309574Sglebius   of countries are ordinarily not used, to avoid incompatibilities
68309574Sglebius   when countries change their name (e.g. Zaire->Congo) or when
69309574Sglebius   locations change countries (e.g. Hong Kong from UK colony to
70309574Sglebius   China).
71309574Sglebius
72309574Sglebius * Be portable to a wide variety of implementations.
73309574Sglebius
74309574Sglebius * Use a consistent naming conventions over the entire world.
75309574Sglebius
76309574SglebiusNames normally have the form AREA/LOCATION, where AREA is the name
77309574Sglebiusof a continent or ocean, and LOCATION is the name of a specific
78309574Sglebiuslocation within that region.  North and South America share the same
79309574Sglebiusarea, 'America'.  Typical names are 'Africa/Cairo', 'America/New_York',
80309574Sglebiusand 'Pacific/Honolulu'.
81309574Sglebius
82309574SglebiusHere are the general rules used for choosing location names,
83309574Sglebiusin decreasing order of importance:
84309574Sglebius
85309574Sglebius	Use only valid POSIX file name components (i.e., the parts of
86309574Sglebius		names other than '/').  Do not use the file name
87309574Sglebius		components '.' and '..'.  Within a file name component,
88309574Sglebius		use only ASCII letters, '.', '-' and '_'.  Do not use
89309574Sglebius		digits, as that might create an ambiguity with POSIX
90309574Sglebius		TZ strings.  A file name component must not exceed 14
91309574Sglebius		characters or start with '-'.  E.g., prefer 'Brunei'
92309574Sglebius		to 'Bandar_Seri_Begawan'.  Exceptions: see the discussion
93309574Sglebius		of legacy names below.
94309574Sglebius	A name must not be empty, or contain '//', or start or end with '/'.
95309574Sglebius	Do not use names that differ only in case.  Although the reference
96309574Sglebius		implementation is case-sensitive, some other implementations
97309574Sglebius		are not, and they would mishandle names differing only in case.
98309574Sglebius	If one name A is an initial prefix of another name AB (ignoring case),
99309574Sglebius		then B must not start with '/', as a regular file cannot have
100309574Sglebius		the same name as a directory in POSIX.  For example,
101309574Sglebius		'America/New_York' precludes 'America/New_York/Bronx'.
102309574Sglebius	Uninhabited regions like the North Pole and Bouvet Island
103309574Sglebius		do not need locations, since local time is not defined there.
104309574Sglebius	There should typically be at least one name for each ISO 3166-1
105309574Sglebius		officially assigned two-letter code for an inhabited country
106309574Sglebius		or territory.
107309574Sglebius	If all the clocks in a region have agreed since 1970,
108309574Sglebius		don't bother to include more than one location
109309574Sglebius		even if subregions' clocks disagreed before 1970.
110309574Sglebius		Otherwise these tables would become annoyingly large.
111309574Sglebius	If a name is ambiguous, use a less ambiguous alternative;
112309574Sglebius		e.g. many cities are named San Jos�� and Georgetown, so
113309574Sglebius		prefer 'Costa_Rica' to 'San_Jose' and 'Guyana' to 'Georgetown'.
114309574Sglebius	Keep locations compact.  Use cities or small islands, not countries
115309574Sglebius		or regions, so that any future time zone changes do not split
116309574Sglebius		locations into different time zones.  E.g. prefer 'Paris'
117309574Sglebius		to 'France', since France has had multiple time zones.
118309574Sglebius	Use mainstream English spelling, e.g. prefer 'Rome' to 'Roma', and
119309574Sglebius		prefer 'Athens' to the Greek '����������' or the Romanized 'Ath��na'.
120309574Sglebius		The POSIX file name restrictions encourage this rule.
121309574Sglebius	Use the most populous among locations in a zone,
122309574Sglebius		e.g. prefer 'Shanghai' to 'Beijing'.  Among locations with
123309574Sglebius		similar populations, pick the best-known location,
124309574Sglebius		e.g. prefer 'Rome' to 'Milan'.
125309574Sglebius	Use the singular form, e.g. prefer 'Canary' to 'Canaries'.
126309574Sglebius	Omit common suffixes like '_Islands' and '_City', unless that
127309574Sglebius		would lead to ambiguity.  E.g. prefer 'Cayman' to
128309574Sglebius		'Cayman_Islands' and 'Guatemala' to 'Guatemala_City',
129309574Sglebius		but prefer 'Mexico_City' to 'Mexico' because the country
130309574Sglebius		of Mexico has several time zones.
131309574Sglebius	Use '_' to represent a space.
132309574Sglebius	Omit '.' from abbreviations in names, e.g. prefer 'St_Helena'
133309574Sglebius		to 'St._Helena'.
134309574Sglebius	Do not change established names if they only marginally
135309574Sglebius		violate the above rules.  For example, don't change
136309574Sglebius		the existing name 'Rome' to 'Milan' merely because
137309574Sglebius		Milan's population has grown to be somewhat greater
138309574Sglebius		than Rome's.
139309574Sglebius	If a name is changed, put its old spelling in the 'backward' file.
140309574Sglebius		This means old spellings will continue to work.
141309574Sglebius
142309574SglebiusThe file 'zone1970.tab' lists geographical locations used to name time
143309574Sglebiuszone rules.  It is intended to be an exhaustive list of names for
144309574Sglebiusgeographic regions as described above; this is a subset of the names
145309574Sglebiusin the data.  Although a 'zone1970.tab' location's longitude
146309574Sglebiuscorresponds to its LMT offset with one hour for every 15 degrees east
147309574Sglebiuslongitude, this relationship is not exact.
148309574Sglebius
149309574SglebiusOlder versions of this package used a different naming scheme,
150309574Sglebiusand these older names are still supported.
151309574SglebiusSee the file 'backward' for most of these older names
152309574Sglebius(e.g., 'US/Eastern' instead of 'America/New_York').
153309574SglebiusThe other old-fashioned names still supported are
154309574Sglebius'WET', 'CET', 'MET', and 'EET' (see the file 'europe').
155309574Sglebius
156309574SglebiusOlder versions of this package defined legacy names that are
157309574Sglebiusincompatible with the first rule of location names, but which are
158309574Sglebiusstill supported.  These legacy names are mostly defined in the file
159309574Sglebius'etcetera'.  Also, the file 'backward' defines the legacy names
160309574Sglebius'GMT0', 'GMT-0', 'GMT+0' and 'Canada/East-Saskatchewan', and the file
161309574Sglebius'northamerica' defines the legacy names 'EST5EDT', 'CST6CDT',
162309574Sglebius'MST7MDT', and 'PST8PDT'.
163309574Sglebius
164309574SglebiusExcluding 'backward' should not affect the other data.  If
165309574Sglebius'backward' is excluded, excluding 'etcetera' should not affect the
166309574Sglebiusremaining data.
167309574Sglebius
168309574Sglebius
169309574Sglebius----- Time zone abbreviations -----
170309574Sglebius
171309574SglebiusWhen this package is installed, it generates time zone abbreviations
172309574Sglebiuslike 'EST' to be compatible with human tradition and POSIX.
173309574SglebiusHere are the general rules used for choosing time zone abbreviations,
174309574Sglebiusin decreasing order of importance:
175309574Sglebius
176309574Sglebius	Use three or more characters that are ASCII alphanumerics or '+' or '-'.
177309574Sglebius		Previous editions of this database also used characters like
178309574Sglebius		' ' and '?', but these characters have a special meaning to
179309574Sglebius		the shell and cause commands like
180309574Sglebius			set `date`
181309574Sglebius		to have unexpected effects.
182309574Sglebius		Previous editions of this rule required upper-case letters,
183309574Sglebius		but the Congressman who introduced Chamorro Standard Time
184309574Sglebius		preferred "ChST", so lower-case letters are now allowed.
185309574Sglebius		Also, POSIX from 2001 on relaxed the rule to allow '-', '+',
186309574Sglebius		and alphanumeric characters from the portable character set
187309574Sglebius		in the current locale.  In practice ASCII alphanumerics and
188309574Sglebius		'+' and '-' are safe in all locales.
189309574Sglebius
190309574Sglebius		In other words, in the C locale the POSIX extended regular
191309574Sglebius		expression [-+[:alnum:]]{3,} should match the abbreviation.
192309574Sglebius		This guarantees that all abbreviations could have been
193309574Sglebius		specified by a POSIX TZ string.
194309574Sglebius
195309574Sglebius	Use abbreviations that are in common use among English-speakers,
196309574Sglebius		e.g. 'EST' for Eastern Standard Time in North America.
197309574Sglebius		We assume that applications translate them to other languages
198309574Sglebius		as part of the normal localization process; for example,
199309574Sglebius		a French application might translate 'EST' to 'HNE'.
200309574Sglebius
201309574Sglebius	For zones whose times are taken from a city's longitude, use the
202309574Sglebius		traditional xMT notation, e.g. 'PMT' for Paris Mean Time.
203309574Sglebius		The only name like this in current use is 'GMT'.
204309574Sglebius
205309574Sglebius	Use 'LMT' for local mean time of locations before the introduction
206309574Sglebius		of standard time; see "Scope of the tz database".
207309574Sglebius
208309574Sglebius	If there is no common English abbreviation, use numeric offsets like
209309574Sglebius		-05 and +0830 that are generated by zic's %z notation.
210309574Sglebius
211309574Sglebius    [The remaining guidelines predate the introduction of %z.
212309574Sglebius    They are problematic as they mean tz data entries invent
213309574Sglebius    notation rather than record it.  These guidelines are now
214309574Sglebius    deprecated and the plan is to gradually move to %z for
215309574Sglebius    inhabited locations and to "-00" for uninhabited locations.]
216309574Sglebius
217309574Sglebius	If there is no common English abbreviation, abbreviate the English
218309574Sglebius		translation of the usual phrase used by native speakers.
219309574Sglebius		If this is not available or is a phrase mentioning the country
220309574Sglebius		(e.g. "Cape Verde Time"), then:
221309574Sglebius
222309574Sglebius		When a country is identified with a single or principal zone,
223309574Sglebius			append 'T' to the country's ISO	code, e.g. 'CVT' for
224309574Sglebius			Cape Verde Time.  For summer time append 'ST';
225309574Sglebius			for double summer time append 'DST'; etc.
226309574Sglebius		Otherwise, take the first three letters of an English place
227309574Sglebius			name identifying each zone and append 'T', 'ST', etc.
228309574Sglebius			as before; e.g. 'VLAST' for VLAdivostok Summer Time.
229309574Sglebius
230309574Sglebius	Use UT (with time zone abbreviation '-00') for locations while
231309574Sglebius		uninhabited.  The leading '-' is a flag that the time
232309574Sglebius		zone is in some sense undefined; this notation is
233309574Sglebius		derived from Internet RFC 3339.
234309574Sglebius
235309574SglebiusApplication writers should note that these abbreviations are ambiguous
236309574Sglebiusin practice: e.g. 'CST' has a different meaning in China than
237309574Sglebiusit does in the United States.  In new applications, it's often better
238309574Sglebiusto use numeric UT offsets like '-0600' instead of time zone
239309574Sglebiusabbreviations like 'CST'; this avoids the ambiguity.
240309574Sglebius
241309574Sglebius
242309574Sglebius----- Accuracy of the tz database -----
243309574Sglebius
244309574SglebiusThe tz database is not authoritative, and it surely has errors.
245309574SglebiusCorrections are welcome and encouraged; see the file CONTRIBUTING.
246309574SglebiusUsers requiring authoritative data should consult national standards
247309574Sglebiusbodies and the references cited in the database's comments.
248309574Sglebius
249309574SglebiusErrors in the tz database arise from many sources:
250309574Sglebius
251309574Sglebius * The tz database predicts future time stamps, and current predictions
252309574Sglebius   will be incorrect after future governments change the rules.
253309574Sglebius   For example, if today someone schedules a meeting for 13:00 next
254309574Sglebius   October 1, Casablanca time, and tomorrow Morocco changes its
255309574Sglebius   daylight saving rules, software can mess up after the rule change
256309574Sglebius   if it blithely relies on conversions made before the change.
257309574Sglebius
258309574Sglebius * The pre-1970 entries in this database cover only a tiny sliver of how
259309574Sglebius   clocks actually behaved; the vast majority of the necessary
260309574Sglebius   information was lost or never recorded.  Thousands more zones would
261309574Sglebius   be needed if the tz database's scope were extended to cover even
262309574Sglebius   just the known or guessed history of standard time; for example,
263309574Sglebius   the current single entry for France would need to split into dozens
264309574Sglebius   of entries, perhaps hundreds.  And in most of the world even this
265309574Sglebius   approach would be misleading due to widespread disagreement or
266309574Sglebius   indifference about what times should be observed.  In her 2015 book
267309574Sglebius   "The Global Transformation of Time, 1870-1950", Vanessa Ogle writes
268309574Sglebius   "Outside of Europe and North America there was no system of time
269309574Sglebius   zones at all, often not even a stable landscape of mean times,
270309574Sglebius   prior to the middle decades of the twentieth century".  See:
271309574Sglebius   Timothy Shenk, Booked: A Global History of Time. Dissent 2015-12-17
272309574Sglebius   https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanessa-ogle
273309574Sglebius
274309574Sglebius * Most of the pre-1970 data entries come from unreliable sources, often
275309574Sglebius   astrology books that lack citations and whose compilers evidently
276309574Sglebius   invented entries when the true facts were unknown, without
277309574Sglebius   reporting which entries were known and which were invented.
278309574Sglebius   These books often contradict each other or give implausible entries,
279309574Sglebius   and on the rare occasions when they are checked they are
280309574Sglebius   typically found to be incorrect.
281309574Sglebius
282309574Sglebius * For the UK the tz database relies on years of first-class work done by
283309574Sglebius   Joseph Myers and others; see <http://www.polyomino.org.uk/british-time/>.
284309574Sglebius   Other countries are not done nearly as well.
285309574Sglebius
286309574Sglebius * Sometimes, different people in the same city would maintain clocks
287309574Sglebius   that differed significantly.  Railway time was used by railroad
288309574Sglebius   companies (which did not always agree with each other),
289309574Sglebius   church-clock time was used for birth certificates, etc.
290309574Sglebius   Often this was merely common practice, but sometimes it was set by law.
291309574Sglebius   For example, from 1891 to 1911 the UT offset in France was legally
292309574Sglebius   0:09:21 outside train stations and 0:04:21 inside.
293309574Sglebius
294309574Sglebius * Although a named location in the tz database stands for the
295309574Sglebius   containing region, its pre-1970 data entries are often accurate for
296309574Sglebius   only a small subset of that region.  For example, Europe/London
297309574Sglebius   stands for the United Kingdom, but its pre-1847 times are valid
298309574Sglebius   only for locations that have London's exact meridian, and its 1847
299309574Sglebius   transition to GMT is known to be valid only for the L&NW and the
300309574Sglebius   Caledonian railways.
301309574Sglebius
302309574Sglebius * The tz database does not record the earliest time for which a zone's
303309574Sglebius   data entries are thereafter valid for every location in the region.
304309574Sglebius   For example, Europe/London is valid for all locations in its
305309574Sglebius   region after GMT was made the standard time, but the date of
306309574Sglebius   standardization (1880-08-02) is not in the tz database, other than
307309574Sglebius   in commentary.  For many zones the earliest time of validity is
308309574Sglebius   unknown.
309309574Sglebius
310309574Sglebius * The tz database does not record a region's boundaries, and in many
311309574Sglebius   cases the boundaries are not known.  For example, the zone
312309574Sglebius   America/Kentucky/Louisville represents a region around the city of
313309574Sglebius   Louisville, the boundaries of which are unclear.
314309574Sglebius
315309574Sglebius * Changes that are modeled as instantaneous transitions in the tz
316309574Sglebius   database were often spread out over hours, days, or even decades.
317309574Sglebius
318309574Sglebius * Even if the time is specified by law, locations sometimes
319309574Sglebius   deliberately flout the law.
320309574Sglebius
321309574Sglebius * Early timekeeping practices, even assuming perfect clocks, were
322309574Sglebius   often not specified to the accuracy that the tz database requires.
323309574Sglebius
324309574Sglebius * Sometimes historical timekeeping was specified more precisely
325309574Sglebius   than what the tz database can handle.  For example, from 1909 to
326309574Sglebius   1937 Netherlands clocks were legally UT +00:19:32.13, but the tz
327309574Sglebius   database cannot represent the fractional second.
328309574Sglebius
329309574Sglebius * Even when all the timestamp transitions recorded by the tz database
330309574Sglebius   are correct, the tz rules that generate them may not faithfully
331309574Sglebius   reflect the historical rules.  For example, from 1922 until World
332309574Sglebius   War II the UK moved clocks forward the day following the third
333309574Sglebius   Saturday in April unless that was Easter, in which case it moved
334309574Sglebius   clocks forward the previous Sunday.  Because the tz database has no
335309574Sglebius   way to specify Easter, these exceptional years are entered as
336309574Sglebius   separate tz Rule lines, even though the legal rules did not change.
337309574Sglebius
338309574Sglebius * The tz database models pre-standard time using the proleptic Gregorian
339309574Sglebius   calendar and local mean time (LMT), but many people used other
340309574Sglebius   calendars and other timescales.  For example, the Roman Empire used
341309574Sglebius   the Julian calendar, and had 12 varying-length daytime hours with a
342309574Sglebius   non-hour-based system at night.
343309574Sglebius
344309574Sglebius * Early clocks were less reliable, and data entries do not represent
345309574Sglebius   this unreliability.
346309574Sglebius
347309574Sglebius * As for leap seconds, civil time was not based on atomic time before
348309574Sglebius   1972, and we don't know the history of earth's rotation accurately
349309574Sglebius   enough to map SI seconds to historical solar time to more than
350309574Sglebius   about one-hour accuracy.  See: Morrison LV, Stephenson FR.
351309574Sglebius   Historical values of the Earth's clock error Delta T and the
352309574Sglebius   calculation of eclipses. J Hist Astron. 2004;35:327-36
353309574Sglebius   <http://adsabs.harvard.edu/full/2004JHA....35..327M>;
354309574Sglebius   Historical values of the Earth's clock error. J Hist Astron. 2005;36:339
355309574Sglebius   <http://adsabs.harvard.edu/full/2005JHA....36..339M>.
356309574Sglebius
357309574Sglebius * The relationship between POSIX time (that is, UTC but ignoring leap
358309574Sglebius   seconds) and UTC is not agreed upon after 1972.  Although the POSIX
359309574Sglebius   clock officially stops during an inserted leap second, at least one
360309574Sglebius   proposed standard has it jumping back a second instead; and in
361309574Sglebius   practice POSIX clocks more typically either progress glacially during
362309574Sglebius   a leap second, or are slightly slowed while near a leap second.
363309574Sglebius
364309574Sglebius * The tz database does not represent how uncertain its information is.
365309574Sglebius   Ideally it would contain information about when data entries are
366309574Sglebius   incomplete or dicey.  Partial temporal knowledge is a field of
367309574Sglebius   active research, though, and it's not clear how to apply it here.
368309574Sglebius
369309574SglebiusIn short, many, perhaps most, of the tz database's pre-1970 and future
370309574Sglebiustime stamps are either wrong or misleading.  Any attempt to pass the
371309574Sglebiustz database off as the definition of time should be unacceptable to
372309574Sglebiusanybody who cares about the facts.  In particular, the tz database's
373309574SglebiusLMT offsets should not be considered meaningful, and should not prompt
374309574Sglebiuscreation of zones merely because two locations differ in LMT or
375309574Sglebiustransitioned to standard time at different dates.
376309574Sglebius
377309574Sglebius
378309574Sglebius----- Time and date functions -----
379309574Sglebius
380309574SglebiusThe tz code contains time and date functions that are upwards
381309574Sglebiuscompatible with those of POSIX.
382309574Sglebius
383309574SglebiusPOSIX has the following properties and limitations.
384309574Sglebius
385309574Sglebius*	In POSIX, time display in a process is controlled by the
386309574Sglebius	environment variable TZ.  Unfortunately, the POSIX TZ string takes
387309574Sglebius	a form that is hard to describe and is error-prone in practice.
388309574Sglebius	Also, POSIX TZ strings can't deal with other (for example, Israeli)
389309574Sglebius	daylight saving time rules, or situations where more than two
390309574Sglebius	time zone abbreviations are used in an area.
391309574Sglebius
392309574Sglebius	The POSIX TZ string takes the following form:
393309574Sglebius
394309574Sglebius		stdoffset[dst[offset][,date[/time],date[/time]]]
395309574Sglebius
396309574Sglebius	where:
397309574Sglebius
398309574Sglebius	std and dst
399309574Sglebius		are 3 or more characters specifying the standard
400309574Sglebius		and daylight saving time (DST) zone names.
401309574Sglebius		Starting with POSIX.1-2001, std and dst may also be
402309574Sglebius		in a quoted form like "<UTC+10>"; this allows
403309574Sglebius		"+" and "-" in the names.
404309574Sglebius	offset
405309574Sglebius		is of the form '[+-]hh:[mm[:ss]]' and specifies the
406309574Sglebius		offset west of UT.  'hh' may be a single digit; 0<=hh<=24.
407309574Sglebius		The default DST offset is one hour ahead of standard time.
408309574Sglebius	date[/time],date[/time]
409309574Sglebius		specifies the beginning and end of DST.  If this is absent,
410309574Sglebius		the system supplies its own rules for DST, and these can
411309574Sglebius		differ from year to year; typically US DST rules are used.
412309574Sglebius	time
413309574Sglebius		takes the form 'hh:[mm[:ss]]' and defaults to 02:00.
414309574Sglebius		This is the same format as the offset, except that a
415309574Sglebius		leading '+' or '-' is not allowed.
416309574Sglebius	date
417309574Sglebius		takes one of the following forms:
418309574Sglebius		Jn (1<=n<=365)
419309574Sglebius			origin-1 day number not counting February 29
420309574Sglebius		n (0<=n<=365)
421309574Sglebius			origin-0 day number counting February 29 if present
422309574Sglebius		Mm.n.d (0[Sunday]<=d<=6[Saturday], 1<=n<=5, 1<=m<=12)
423309574Sglebius			for the dth day of week n of month m of the year,
424309574Sglebius			where week 1 is the first week in which day d appears,
425309574Sglebius			and '5' stands for the last week in which day d appears
426309574Sglebius			(which may be either the 4th or 5th week).
427309574Sglebius			Typically, this is the only useful form;
428309574Sglebius			the n and Jn forms are rarely used.
429309574Sglebius
430309574Sglebius	Here is an example POSIX TZ string, for US Pacific time using rules
431309574Sglebius	appropriate from 1987 through 2006:
432309574Sglebius
433309574Sglebius		TZ='PST8PDT,M4.1.0/02:00,M10.5.0/02:00'
434309574Sglebius
435309574Sglebius	This POSIX TZ string is hard to remember, and mishandles time stamps
436309574Sglebius	before 1987 and after 2006.  With this package you can use this
437309574Sglebius	instead:
438309574Sglebius
439309574Sglebius		TZ='America/Los_Angeles'
440309574Sglebius
441309574Sglebius*	POSIX does not define the exact meaning of TZ values like "EST5EDT".
442309574Sglebius	Typically the current US DST rules are used to interpret such values,
443309574Sglebius	but this means that the US DST rules are compiled into each program
444309574Sglebius	that does time conversion.  This means that when US time conversion
445309574Sglebius	rules change (as in the United States in 1987), all programs that
446309574Sglebius	do time conversion must be recompiled to ensure proper results.
447309574Sglebius
448309574Sglebius*	The TZ environment variable is process-global, which makes it hard
449309574Sglebius	to write efficient, thread-safe applications that need access
450309574Sglebius	to multiple time zones.
451309574Sglebius
452309574Sglebius*	In POSIX, there's no tamper-proof way for a process to learn the
453309574Sglebius	system's best idea of local wall clock.  (This is important for
454309574Sglebius	applications that an administrator wants used only at certain times -
455309574Sglebius	without regard to whether the user has fiddled the "TZ" environment
456309574Sglebius	variable.  While an administrator can "do everything in UTC" to get
457309574Sglebius	around the problem, doing so is inconvenient and precludes handling
458309574Sglebius	daylight saving time shifts - as might be required to limit phone
459309574Sglebius	calls to off-peak hours.)
460309574Sglebius
461309574Sglebius*	POSIX provides no convenient and efficient way to determine the UT
462309574Sglebius	offset and time zone abbreviation of arbitrary time stamps,
463309574Sglebius	particularly for time zone settings that do not fit into the
464309574Sglebius	POSIX model.
465309574Sglebius
466309574Sglebius*	POSIX requires that systems ignore leap seconds.
467309574Sglebius
468309574Sglebius*	The tz code attempts to support all the time_t implementations
469309574Sglebius	allowed by POSIX.  The time_t type represents a nonnegative count of
470309574Sglebius	seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds.
471309574Sglebius	In practice, time_t is usually a signed 64- or 32-bit integer; 32-bit
472309574Sglebius	signed time_t values stop working after 2038-01-19 03:14:07 UTC, so
473309574Sglebius	new implementations these days typically use a signed 64-bit integer.
474309574Sglebius	Unsigned 32-bit integers are used on one or two platforms,
475309574Sglebius	and 36-bit and 40-bit integers are also used occasionally.
476309574Sglebius	Although earlier POSIX versions allowed time_t to be a
477309574Sglebius	floating-point type, this was not supported by any practical
478309574Sglebius	systems, and POSIX.1-2013 and the tz code both require time_t
479309574Sglebius	to be an integer type.
480309574Sglebius
481309574SglebiusThese are the extensions that have been made to the POSIX functions:
482309574Sglebius
483309574Sglebius*	The "TZ" environment variable is used in generating the name of a file
484309574Sglebius	from which time zone information is read (or is interpreted a la
485309574Sglebius	POSIX); "TZ" is no longer constrained to be a three-letter time zone
486309574Sglebius	name followed by a number of hours and an optional three-letter
487309574Sglebius	daylight time zone name.  The daylight saving time rules to be used
488309574Sglebius	for a particular time zone are encoded in the time zone file;
489309574Sglebius	the format of the file allows U.S., Australian, and other rules to be
490309574Sglebius	encoded, and allows for situations where more than two time zone
491309574Sglebius	abbreviations are used.
492309574Sglebius
493309574Sglebius	It was recognized that allowing the "TZ" environment variable to
494309574Sglebius	take on values such as "America/New_York" might cause "old" programs
495309574Sglebius	(that expect "TZ" to have a certain form) to operate incorrectly;
496309574Sglebius	consideration was given to using some other environment variable
497309574Sglebius	(for example, "TIMEZONE") to hold the string used to generate the
498309574Sglebius	time zone information file name.  In the end, however, it was decided
499309574Sglebius	to continue using "TZ": it is widely used for time zone purposes;
500309574Sglebius	separately maintaining both "TZ" and "TIMEZONE" seemed a nuisance;
501309574Sglebius	and systems where "new" forms of "TZ" might cause problems can simply
502309574Sglebius	use TZ values such as "EST5EDT" which can be used both by
503309574Sglebius	"new" programs (a la POSIX) and "old" programs (as zone names and
504309574Sglebius	offsets).
505309574Sglebius
506309574Sglebius*	The code supports platforms with a UT offset member in struct tm,
507309574Sglebius	e.g., tm_gmtoff.
508309574Sglebius
509309574Sglebius*	The code supports platforms with a time zone abbreviation member in
510309574Sglebius	struct tm, e.g., tm_zone.
511309574Sglebius
512309574Sglebius*	Since the "TZ" environment variable can now be used to control time
513309574Sglebius	conversion, the "daylight" and "timezone" variables are no longer
514309574Sglebius	needed.  (These variables are defined and set by "tzset"; however, their
515309574Sglebius	values will not be used by "localtime.")
516309574Sglebius
517309574Sglebius*	Functions tzalloc, tzfree, localtime_rz, and mktime_z for
518309574Sglebius	more-efficient thread-safe applications that need to use
519309574Sglebius	multiple time zones.  The tzalloc and tzfree functions
520309574Sglebius	allocate and free objects of type timezone_t, and localtime_rz
521309574Sglebius	and mktime_z are like localtime_r and mktime with an extra
522309574Sglebius	timezone_t argument.  The functions were inspired by NetBSD.
523309574Sglebius
524309574Sglebius*	A function "tzsetwall" has been added to arrange for the system's
525309574Sglebius	best approximation to local wall clock time to be delivered by
526309574Sglebius	subsequent calls to "localtime."  Source code for portable
527309574Sglebius	applications that "must" run on local wall clock time should call
528309574Sglebius	"tzsetwall();" if such code is moved to "old" systems that don't
529309574Sglebius	provide tzsetwall, you won't be able to generate an executable program.
530309574Sglebius	(These time zone functions also arrange for local wall clock time to be
531309574Sglebius	used if tzset is called - directly or indirectly - and there's no "TZ"
532309574Sglebius	environment variable; portable applications should not, however, rely
533309574Sglebius	on this behavior since it's not the way SVR2 systems behave.)
534309574Sglebius
535309574Sglebius*	Negative time_t values are supported, on systems where time_t is signed.
536309574Sglebius
537309574Sglebius*	These functions can account for leap seconds, thanks to Bradley White.
538309574Sglebius
539309574SglebiusPoints of interest to folks with other systems:
540309574Sglebius
541309574Sglebius*	Code compatible with this package is already part of many platforms,
542309574Sglebius	including GNU/Linux, Android, the BSDs, Chromium OS, Cygwin, AIX, iOS,
543309574Sglebius	BlackBery 10, macOS, Microsoft Windows, OpenVMS, and Solaris.
544309574Sglebius	On such hosts, the primary use of this package
545309574Sglebius	is to update obsolete time zone rule tables.
546309574Sglebius	To do this, you may need to compile the time zone compiler
547309574Sglebius	'zic' supplied with this package instead of using the system 'zic',
548309574Sglebius	since the format of zic's input is occasionally extended,
549309574Sglebius	and a platform may still be shipping an older zic.
550309574Sglebius
551309574Sglebius*	The UNIX Version 7 "timezone" function is not present in this package;
552309574Sglebius	it's impossible to reliably map timezone's arguments (a "minutes west
553309574Sglebius	of GMT" value and a "daylight saving time in effect" flag) to a
554309574Sglebius	time zone abbreviation, and we refuse to guess.
555309574Sglebius	Programs that in the past used the timezone function may now examine
556309574Sglebius	tzname[localtime(&clock)->tm_isdst] to learn the correct time
557309574Sglebius	zone abbreviation to use.  Alternatively, use
558309574Sglebius	localtime(&clock)->tm_zone if this has been enabled.
559309574Sglebius
560309574Sglebius*	The 4.2BSD gettimeofday function is not used in this package.
561309574Sglebius	This formerly let users obtain the current UTC offset and DST flag,
562309574Sglebius	but this functionality was removed in later versions of BSD.
563309574Sglebius
564309574Sglebius*	In SVR2, time conversion fails for near-minimum or near-maximum
565309574Sglebius	time_t values when doing conversions for places that don't use UT.
566309574Sglebius	This package takes care to do these conversions correctly.
567309574Sglebius	A comment in the source code tells how to get compatibly wrong
568309574Sglebius	results.
569309574Sglebius
570309574SglebiusThe functions that are conditionally compiled if STD_INSPIRED is defined
571309574Sglebiusshould, at this point, be looked on primarily as food for thought.  They are
572309574Sglebiusnot in any sense "standard compatible" - some are not, in fact, specified in
573309574Sglebius*any* standard.  They do, however, represent responses of various authors to
574309574Sglebiusstandardization proposals.
575309574Sglebius
576309574SglebiusOther time conversion proposals, in particular the one developed by folks at
577309574SglebiusHewlett Packard, offer a wider selection of functions that provide capabilities
578309574Sglebiusbeyond those provided here.  The absence of such functions from this package
579309574Sglebiusis not meant to discourage the development, standardization, or use of such
580309574Sglebiusfunctions.  Rather, their absence reflects the decision to make this package
581309574Sglebiuscontain valid extensions to POSIX, to ensure its broad acceptability.  If
582309574Sglebiusmore powerful time conversion functions can be standardized, so much the
583309574Sglebiusbetter.
584309574Sglebius
585309574Sglebius
586309574Sglebius----- Interface stability -----
587309574Sglebius
588309574SglebiusThe tz code and data supply the following interfaces:
589309574Sglebius
590309574Sglebius * A set of zone names as per "Names of time zone rules" above.
591309574Sglebius
592309574Sglebius * Library functions described in "Time and date functions" above.
593309574Sglebius
594309574Sglebius * The programs tzselect, zdump, and zic, documented in their man pages.
595309574Sglebius
596309574Sglebius * The format of zic input files, documented in the zic man page.
597309574Sglebius
598309574Sglebius * The format of zic output files, documented in the tzfile man page.
599309574Sglebius
600309574Sglebius * The format of zone table files, documented in zone1970.tab.
601309574Sglebius
602309574Sglebius * The format of the country code file, documented in iso3166.tab.
603309574Sglebius
604309574SglebiusWhen these interfaces are changed, an effort is made to preserve
605309574Sglebiusbackward compatibility.  For example, tz data files typically do not
606309574Sglebiusrely on recently-added zic features, so that users can run older zic
607309574Sglebiusversions to process newer data files.
608309574Sglebius
609309574SglebiusInterfaces not listed above are less stable.  For example, users
610309574Sglebiusshould not rely on particular UT offsets or abbreviations for time
611309574Sglebiusstamps, as data entries are often based on guesswork and these guesses
612309574Sglebiusmay be corrected or improved.
613309574Sglebius
614309574Sglebius
615309574Sglebius----- Calendrical issues -----
616309574Sglebius
617309574SglebiusCalendrical issues are a bit out of scope for a time zone database,
618309574Sglebiusbut they indicate the sort of problems that we would run into if we
619309574Sglebiusextended the time zone database further into the past.  An excellent
620309574Sglebiusresource in this area is Nachum Dershowitz and Edward M. Reingold,
621309574SglebiusCalendrical Calculations: Third Edition, Cambridge University Press (2008)
622309574Sglebius<http://emr.cs.iit.edu/home/reingold/calendar-book/third-edition/>.
623309574SglebiusOther information and sources are given below.  They sometimes disagree.
624309574Sglebius
625309574Sglebius
626309574SglebiusFrance
627309574Sglebius
628309574SglebiusGregorian calendar adopted 1582-12-20.
629309574SglebiusFrench Revolutionary calendar used 1793-11-24 through 1805-12-31,
630309574Sglebiusand (in Paris only) 1871-05-06 through 1871-05-23.
631309574Sglebius
632309574Sglebius
633309574SglebiusRussia
634309574Sglebius
635309574SglebiusFrom Chris Carrier (1996-12-02):
636309574SglebiusOn 1929-10-01 the Soviet Union instituted an "Eternal Calendar"
637309574Sglebiuswith 30-day months plus 5 holidays, with a 5-day week.
638309574SglebiusOn 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the
639309574SglebiusGregorian calendar while retaining the 6-day week; on 1940-06-27 it
640309574Sglebiusreverted to the 7-day week.  With the 6-day week the usual days
641309574Sglebiusoff were the 6th, 12th, 18th, 24th and 30th of the month.
642309574Sglebius(Source: Evitiar Zerubavel, _The Seven Day Circle_)
643309574Sglebius
644309574Sglebius
645309574SglebiusMark Brader reported a similar story in "The Book of Calendars", edited
646309574Sglebiusby Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377.  But:
647309574Sglebius
648309574SglebiusFrom: Petteri Sulonen (via Usenet)
649309574SglebiusDate: 14 Jan 1999 00:00:00 GMT
650309574Sglebius...
651309574Sglebius
652309574SglebiusIf your source is correct, how come documents between 1929 and 1940 were
653309574Sglebiusstill dated using the conventional, Gregorian calendar?
654309574Sglebius
655309574SglebiusI can post a scan of a document dated December 1, 1934, signed by
656309574SglebiusYenukidze, the secretary, on behalf of Kalinin, the President of the
657309574SglebiusExecutive Committee of the Supreme Soviet, if you like.
658309574Sglebius
659309574Sglebius
660309574Sglebius
661309574SglebiusSweden (and Finland)
662309574Sglebius
663309574SglebiusFrom: Mark Brader
664309574SglebiusSubject: Re: Gregorian reform - a part of locale?
665309574Sglebius<news:1996Jul6.012937.29190@sq.com>
666309574SglebiusDate: 1996-07-06
667309574Sglebius
668309574SglebiusIn 1700, Denmark made the transition from Julian to Gregorian.  Sweden
669309574Sglebiusdecided to *start* a transition in 1700 as well, but rather than have one of
670309574Sglebiusthose unsightly calendar gaps :-), they simply decreed that the next leap
671309574Sglebiusyear after 1696 would be in 1744 - putting the whole country on a calendar
672309574Sglebiusdifferent from both Julian and Gregorian for a period of 40 years.
673309574Sglebius
674309574SglebiusHowever, in 1704 something went wrong and the plan was not carried through;
675309574Sglebiusthey did, after all, have a leap year that year.  And one in 1708.  In 1712
676309574Sglebiusthey gave it up and went back to Julian, putting 30 days in February that
677309574Sglebiusyear!...
678309574Sglebius
679309574SglebiusThen in 1753, Sweden made the transition to Gregorian in the usual manner,
680309574Sglebiusgetting there only 13 years behind the original schedule.
681309574Sglebius
682309574Sglebius(A previous posting of this story was challenged, and Swedish readers
683309574Sglebiusproduced the following references to support it: "Tider��kning och historia"
684309574Sglebiusby Natanael Beckman (1924) and "Tid, en bok om tider��kning och
685309574Sglebiuskalenderv��sen" by Lars-Olof Lod��n (1968).
686309574Sglebius
687309574Sglebius
688309574SglebiusGrotefend's data
689309574Sglebius
690309574SglebiusFrom: "Michael Palmer" [with one obvious typo fixed]
691309574SglebiusSubject: Re: Gregorian Calendar (was Re: Another FHC related question
692309574SglebiusNewsgroups: soc.genealogy.german
693309574SglebiusDate: Tue, 9 Feb 1999 02:32:48 -800
694309574Sglebius...
695309574Sglebius
696309574SglebiusThe following is a(n incomplete) listing, arranged chronologically, of
697309574SglebiusEuropean states, with the date they converted from the Julian to the
698309574SglebiusGregorian calendar:
699309574Sglebius
700309574Sglebius04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman
701309574Sglebius                 Catholics and Danzig only)
702309574Sglebius09/20 Dec 1582 - France, Lorraine
703309574Sglebius
704309574Sglebius21 Dec 1582/
705309574Sglebius   01 Jan 1583 - Holland, Brabant, Flanders, Hennegau
706309574Sglebius10/21 Feb 1583 - bishopric of Liege (L��ttich)
707309574Sglebius13/24 Feb 1583 - bishopric of Augsburg
708309574Sglebius04/15 Oct 1583 - electorate of Trier
709309574Sglebius05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg,
710309574Sglebius                 Salzburg, Brixen
711309574Sglebius13/24 Oct 1583 - Austrian Oberelsa�� and Breisgau
712309574Sglebius20/31 Oct 1583 - bishopric of Basel
713309574Sglebius02/13 Nov 1583 - duchy of J��lich-Berg
714309574Sglebius02/13 Nov 1583 - electorate and city of K��ln
715309574Sglebius04/15 Nov 1583 - bishopric of W��rzburg
716309574Sglebius11/22 Nov 1583 - electorate of Mainz
717309574Sglebius16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden
718309574Sglebius17/28 Nov 1583 - bishopric of M��nster and duchy of Cleve
719309574Sglebius14/25 Dec 1583 - Steiermark
720309574Sglebius
721309574Sglebius06/17 Jan 1584 - Austria and Bohemia
722309574Sglebius11/22 Jan 1584 - Lucerne, Uri, Schwyz, Zug, Freiburg, Solothurn
723309574Sglebius12/23 Jan 1584 - Silesia and the Lausitz
724309574Sglebius22 Jan/
725309574Sglebius   02 Feb 1584 - Hungary (legally on 21 Oct 1587)
726309574Sglebius      Jun 1584 - Unterwalden
727309574Sglebius01/12 Jul 1584 - duchy of Westfalen
728309574Sglebius
729309574Sglebius16/27 Jun 1585 - bishopric of Paderborn
730309574Sglebius
731309574Sglebius14/25 Dec 1590 - Transylvania
732309574Sglebius
733309574Sglebius22 Aug/
734309574Sglebius   02 Sep 1612 - duchy of Prussia
735309574Sglebius
736309574Sglebius13/24 Dec 1614 - Pfalz-Neuburg
737309574Sglebius
738309574Sglebius          1617 - duchy of Kurland (reverted to the Julian calendar in
739309574Sglebius                 1796)
740309574Sglebius
741309574Sglebius          1624 - bishopric of Osnabr��ck
742309574Sglebius
743309574Sglebius          1630 - bishopric of Minden
744309574Sglebius
745309574Sglebius15/26 Mar 1631 - bishopric of Hildesheim
746309574Sglebius
747309574Sglebius          1655 - Kanton Wallis
748309574Sglebius
749309574Sglebius05/16 Feb 1682 - city of Strassburg
750309574Sglebius
751309574Sglebius18 Feb/
752309574Sglebius   01 Mar 1700 - Protestant Germany (including Swedish possessions in
753309574Sglebius                 Germany), Denmark, Norway
754309574Sglebius30 Jun/
755309574Sglebius   12 Jul 1700 - Gelderland, Zutphen
756309574Sglebius10 Nov/
757309574Sglebius   12 Dec 1700 - Utrecht, Overijssel
758309574Sglebius
759309574Sglebius31 Dec 1700/
760309574Sglebius   12 Jan 1701 - Friesland, Groningen, Z��rich, Bern, Basel, Geneva,
761309574Sglebius                 Turgau, and Schaffhausen
762309574Sglebius
763309574Sglebius          1724 - Glarus, Appenzell, and the city of St. Gallen
764309574Sglebius
765309574Sglebius01 Jan 1750    - Pisa and Florence
766309574Sglebius
767309574Sglebius02/14 Sep 1752 - Great Britain
768309574Sglebius
769309574Sglebius17 Feb/
770309574Sglebius   01 Mar 1753 - Sweden
771309574Sglebius
772309574Sglebius1760-1812      - Graub��nden
773309574Sglebius
774309574SglebiusThe Russian empire (including Finland and the Baltic states) did not
775309574Sglebiusconvert to the Gregorian calendar until the Soviet revolution of 1917.
776309574Sglebius
777309574SglebiusSource: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen
778309574SglebiusMittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend
779309574Sglebius(Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28.
780309574Sglebius
781309574Sglebius
782309574Sglebius----- Time and time zones on Mars -----
783309574Sglebius
784309574SglebiusSome people's work schedules use Mars time.  Jet Propulsion Laboratory
785309574Sglebius(JPL) coordinators have kept Mars time on and off at least since 1997
786309574Sglebiusfor the Mars Pathfinder mission.  Some of their family members have
787309574Sglebiusalso adapted to Mars time.  Dozens of special Mars watches were built
788309574Sglebiusfor JPL workers who kept Mars time during the Mars Exploration
789309574SglebiusRovers mission (2004).  These timepieces look like normal Seikos and
790309574SglebiusCitizens but use Mars seconds rather than terrestrial seconds.
791309574Sglebius
792309574SglebiusA Mars solar day is called a "sol" and has a mean period equal to
793309574Sglebiusabout 24 hours 39 minutes 35.244 seconds in terrestrial time.  It is
794309574Sglebiusdivided into a conventional 24-hour clock, so each Mars second equals
795309574Sglebiusabout 1.02749125 terrestrial seconds.
796309574Sglebius
797309574SglebiusThe prime meridian of Mars goes through the center of the crater
798309574SglebiusAiry-0, named in honor of the British astronomer who built the
799309574SglebiusGreenwich telescope that defines Earth's prime meridian.  Mean solar
800309574Sglebiustime on the Mars prime meridian is called Mars Coordinated Time (MTC).
801309574Sglebius
802309574SglebiusEach landed mission on Mars has adopted a different reference for
803309574Sglebiussolar time keeping, so there is no real standard for Mars time zones.
804309574SglebiusFor example, the Mars Exploration Rover project (2004) defined two
805309574Sglebiustime zones "Local Solar Time A" and "Local Solar Time B" for its two
806309574Sglebiusmissions, each zone designed so that its time equals local true solar
807309574Sglebiustime at approximately the middle of the nominal mission.  Such a "time
808309574Sglebiuszone" is not particularly suited for any application other than the
809309574Sglebiusmission itself.
810309574Sglebius
811309574SglebiusMany calendars have been proposed for Mars, but none have achieved
812309574Sglebiuswide acceptance.  Astronomers often use Mars Sol Date (MSD) which is a
813309574Sglebiussequential count of Mars solar days elapsed since about 1873-12-29
814309574Sglebius12:00 GMT.
815309574Sglebius
816309574SglebiusThe tz database does not currently support Mars time, but it is
817309574Sglebiusdocumented here in the hopes that support will be added eventually.
818309574Sglebius
819309574SglebiusSources:
820309574Sglebius
821309574SglebiusMichael Allison and Robert Schmunk,
822309574Sglebius"Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock"
823309574Sglebius<http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2012-08-08).
824309574Sglebius
825309574SglebiusJia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times
826309574Sglebius<http://articles.latimes.com/2004/jan/14/science/sci-marstime14>
827309574Sglebius(2004-01-14), pp A1, A20-A21.
828309574Sglebius
829309574SglebiusTom Chmielewski, "Jet Lag Is Worse on Mars", The Atlantic (2015-02-26)
830309574Sglebius<http://www.theatlantic.com/technology/archive/2015/02/jet-lag-is-worse-on-mars/386033/>
831309574Sglebius
832309574Sglebius-----
833309574Sglebius
834309574SglebiusThis file is in the public domain, so clarified as of 2009-05-17 by
835309574SglebiusArthur David Olson.
836309574Sglebius
837309574Sglebius-----
838309574SglebiusLocal Variables:
839309574Sglebiuscoding: utf-8
840309574SglebiusEnd:
841