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Proposed patch - Theory notes for backward file
by Stephen Colebourne Sept. 5, 2013

Sept. 5, 2013

Theory notes for backward file Note that the file exists for compatibility and canonicalization Explicitly note IDs in that file are deprecated Explicitly note that data set should make sense without backward ---------------- https://github.com/jodastephen/tz/commit/709e51dc7aeea8c2286b8a50c0d91d475b… The aim of this patch is simple - to document what the backward file is for in more detail. Stephen ---------------- @@ -362,12 +362,19 @@ constraints. Although a 'zone.tab' location's longitude corresponds to its LMT offset with one hour for every 15 degrees east longitude, this relationship is not exact and is not true for 'time.tab'. +The file 'backward' consists of Link entries mapping deprecated names +to their replacements. Usage of a deprecated name is discouraged. +As such, the file permits canonicalization, where the use of a +deprecated name can be automatically replaced with the replacement. +If the data set is used with the 'backward' file file excluded, then +it must remain logical and complete. For example, there must be no +references to any deprecated name from any other file. + Older versions of this package used a different naming scheme, -and these older names are still supported. -See the file 'backward' for most of these older names +and these older names are still supported using 'backward'. (e.g. 'US/Eastern' instead of 'America/New_York'). -The other old-fashioned names still supported are -'WET', 'CET', 'MET', and 'EET' (see the file 'europe'). +Some other old-fashioned names are not deprecated, such as +'WET', 'CET', 'MET', and 'EET', see the 'europe' file.

5 11

Proposed patch - Theory change to reinstate reference to ISO-3166
by Stephen Colebourne Sept. 5, 2013

Sept. 5, 2013

Theory change to reinstate reference to ISO-3166 Use ISO-3166 as a guide for when a name should exist Countries are not specified and nothing is mandated -------------------------- https://github.com/jodastephen/tz/commit/e6199cc2616e938efb9422b263bd09da70… This patch reinstates the link to ISO-3166 in a softer way. In my opinion, the original removal (of something present for 16 years) did not have consensus and should have been reverted. However, I offer this patch as a possible middle ground. Stephen -------------------------- @@ -316,6 +316,8 @@ in decreasing order of importance: 'America/New_York' precludes 'America/New_York/Bronx'. Uninhabited regions like the North Pole and Bouvet Island do not need locations, since local time is not defined there. + Use ISO-3166 as a guide to ensuring time zone name coverage. + There should typically be at least one name per ISO-3166 code. If all the clocks in a region have agreed since 1970, don't bother to include more than one location even if subregions' clocks disagreed before 1970.

5 7

State of the tzdb
by Stephen Colebourne Sept. 4, 2013

Sept. 4, 2013

We're a lot further forward now to regaining stability, but there are a few points still outstanding. 1) Should there be one zone ID in the main files (not "backward") for each inhabited ISO-3166 code? I've argued for this as a reinstatement of a rule of 16 years standing which is no more than common sense. Paul has argued against. 2) Zone ID for America/Shiprock Reinstate Yes/No? 3) Zone ID for Antarctica/South_Pole Reinstate Yes/No? At a minimum, the "backward" link needs to point to McMurdo 4) Recognise correct usage of "backward" file As per ECMAscript: http://norbertlindenberg.com/ecmascript/intl.html#sec-6.4.2 the "backward" is, and will continue to be, used for canonicalization - ie. identifying which IDs can be normalized away. As such, the tzdb needs to be very careful about cross-ISO-3166 links placed in the "backward" file (IMO there should be none to avoid political offence via canonicalization). The use of "backward" should be further documented in Theory to indicate its usage as a canonicalization file, and to indicate that the entire tzdb data set must make sense if the "backward" file is not processed (thus no lines in zone.tab should point to an ID in "backward") 5) Pre-1970 data Some of this seems uncontroversial at this point (don't remove data, don't create new IDs just for pre-1970). Some of it is still under discussion. Only enhancement of existing IDs is necessary to the applications I work with. As noted in the other thread, removing IDs that only differ in LMT is harder than initially thought, as the start of fixed offsets and the name of fixed offsets are pieces of data covered under the no deletion rule. As such, it is unlikely that there are many possibilities for merging zones. 6) ... anything I've forgotten? Finally, I'm sorry I've had to spend so must list time discussing this. Unfortunately, this data is just too important to me and the applications/langauages downstream of me to allow me to not object loudly. thanks Stephen

6 13

[PATCH] Document some longstanding unwritten guidelines.
by Paul Eggert Sept. 3, 2013

Sept. 3, 2013

These come from POSIX or similar platforms, or from the standard 'zic' implementation, but never got written down anywhere. * Theory: Document other POSIX-inspired restrictions on names. * zic.8 (DESCRIPTION): Document that zic's behavior is unspecified if some names are duplicates. Sometimes it complains, sometimes not. --- Theory | 10 ++++++++-- zic.8 | 3 +++ 2 files changed, 11 insertions(+), 2 deletions(-) diff --git a/Theory b/Theory index bd62c5c..b11cbc8 100644 --- a/Theory +++ b/Theory @@ -299,15 +299,21 @@ Here are the general rules used for choosing location names, in decreasing order of importance: Use only valid POSIX file name components (i.e., the parts of - names other than '/'). Within a file name component, + names other than '/'). Do not use the file name + components '.' and '..'. Within a file name component, use only ASCII letters, '.', '-' and '_'. Do not use digits, as that might create an ambiguity with POSIX TZ strings. A file name component must not exceed 14 characters or start with '-'. E.g., prefer 'Brunei' to 'Bandar_Seri_Begawan'. + A name must not be empty, or contain '//', or start or end with '/'. Do not use names that differ only in case. Although the reference - implementation is case-sensitive, some other implementations + implementation is case-sensitive, some other implementations are not, and they would mishandle names differing only in case. + If one name A is an initial prefix of another name AB (ignoring case), + then B must not start with '/', as a regular file cannot have + the same name as a directory in POSIX. For example, + 'America/New_York' precludes 'America/New_York/Bronx'. Uninhabited regions like the North Pole and Bouvet Island do not need locations, since local time is not defined there. If all the clocks in a region have agreed since 1970, diff --git a/zic.8 b/zic.8 index d61555e..d0d34ce 100644 --- a/zic.8 +++ b/zic.8 @@ -362,6 +362,9 @@ field is used as an alternate name for that zone. .PP Except for continuation lines, lines may appear in any order in the input. +However, the behavior is unspecified if multiple zone or link lines +define the same name, or if the source of one link line is the target +of another. .PP Lines in the file that describes leap seconds have the following form: .nf -- 1.8.1.2

1 0

[PATCH 2/3] Replace some zones with links when that doesn't lose non-LMT info.
by Meno Hochschild Sept. 3, 2013

Sept. 3, 2013

*Paul Eggert* eggert at cs.ucla.edu <mailto:tz%40iana.org?Subject=Re:%20Re%3A%20%5Btz%5D%20%5BPATCH%202/3%5D%20Replace%20some%20zones%20with%20links%20when%20that%0A%20doesn%27t%20lose%20non-LMT%20info.&In-Reply-To=%3C522616ED.6060902%40cs.ucla.edu%3E> /Tue Sep 3 17:05:49 UTC 2013/ Lester Caine wrote: >/can we at least agree that the quality of the material is heading in the right direction? / Yes, that's the idea. While I personally have no problem with tidy-up of obviously wrong data and also agree that correction of mistakes is more important than stability (which has never been absolutely pretended), I think end-users of tzdb should get a better opportunity to estimate how reliable the data are and how much trust they can put in their time zone calculations. Offsets in LMT-lines can easily be qualified as UNKNOWN. For the proposed date of 1970 as general separation point between UNSAFE and (apparently) RELIABLE I am not so sure. Would it not be helpful for end-users if there is an additional year-type attribute per zone which tells the users since when the data can be confirmed with high probability of correctness? Would require about 400+ attributes (ok, 1970 as default). I am sure for example in UK or in Germany the data are correct even a pretty while before 1970. Flexibility would be a good thing, isn't it? External APIs could support the users with this extra quality information per offset and make them better aware that historical tz data are not set in stone. Just giving a thought...

3 2

Dealing with Pre-1970 Data
by David Patte ₯ Sept. 3, 2013

Sept. 3, 2013

Though it has been handy to have some pre-1970 data within the tz database, I don't see that it is the best solution for historical tz data in the long run. It is clear that that going back far enough in time there is a different LMT for every 15 seconds of latitude. My own preference would be that historical (and perhaps all tz data) be given a numberic identifier, not a 'America/Someplace' name, for the populated areas in question. A good source of geographic identifiers already available is the geonames database. The tz data for Montreal could be identified by the geonames number for Montreal, and the tz data for Toronto associated with the geoname number for Toronto. Then, to build regions, since all geonames records already have a field for the tz region, these could reflect the numeric identifier of the tz recommended region for each location. For example, Ottawa, in the geonames database would refer to the numeric identifier of Toronto instead of 'America/Toronto', until sometime decides to add historical data for Ottawa's own tz history, at which point it would adopt the identifier for Ottawa.

10 69

Value of data ...
by Lester Caine Sept. 3, 2013

Sept. 3, 2013

Norbert supplied a link to a ecma document which makes interesting reading ... From the section on 'Time Zone Names' > All registered Zone and Link names are allowed. Implementations must recognize all such names, and use > best available current and historical information about their offsets from UTC and their daylight saving time > rules in calculations. Note the use of 'and historical information' here. One has to bare in mind the target data set when deciding what data is useful and what can be thrown away, and for much day to day work a TZ database that only provides future 'estimated' data is probably more than adequate. Banks may be able to get away with 'it's ten years old so we can throw it away' and take control of dormant funds, but for some of us the history is as important as the present day. In fifty years time a large proportion of the data we are creating today will still be available. I dug out material going back 200+ years last night which has now been scanned and archived ... material on 'time' in the Isle of Man for the record ... which helps to clarify calculations for UTC time offsets for material in the early 1900's, which if now stored as UTC normalised data need to be 'corrected' using an historic version of the TZ data. If someone tries to use that data with a 'winnowed' data set, then the wrong times will be returned? Who is to say what an end user is going to be doing with their machine? All right you can reduce 440 zones down to 300 or so, but all of the original 440 names still need to be available, and in these days does saving a few bytes really matter? 'Simplification' of access is more to do with showing the appropriate subset of options by the application and historical ones may actually be the correct answer. So the data should be as complete a record of the 'best available current and historical information' that we have! Providing a version of the data that will be WRONG for some users is not an option? -- Lester Caine - G8HFL ----------------------------- Contact - http://lsces.co.uk/wiki/?page=contact L.S.Caine Electronic Services - http://lsces.co.uk EnquirySolve - http://enquirysolve.com/ Model Engineers Digital Workshop - http://medw.co.uk Rainbow Digital Media - http://rainbowdigitalmedia.co.uk

2 2

[PATCH] Revert recent pre-1970 changes.
by Paul Eggert Sept. 3, 2013

Sept. 3, 2013

Other tz file readers had problems with the new pre1970 file, so remove it and related changes. To recover the pre-1970 data, instead change pre-1970 Zone entries in other files back to what they were. Perhaps we'll try to find a better way someday. * .gitignore: Remove back-pre1970. * Makefile (BACKWARD): Remove. All uses changed back to 'backward'. (AWK_SCRIPTS): Remove back-pre1970.awk. (back-pre1970): Remove. (clean_misc): Don't rm back-pre1970. (check_public): Remove special case for pre1970. * back-pre1970.awk, pre1970: Remove. * backward (America/Anguilla, America/Antigua, America/Aruba) (America/Atikokan, America/Blanc-Sablon, America/Cayman) (America/Creston, America/Curacao, America/Dominica, America/Grenada) (America/Guadeloupe, America/Montreal, America/Montserrat) (America/Nassau, America/Port_of_Spain, America/St_Kitts) (America/St_Lucia, America/St_Thomas, America/St_Vincent) (America/Tortola): Remove, as these are zones again. (America/Coral_Harbour, America/Kralendijk, America/Lower_Princes) (America/Marigot, America/St_Barthelemy, America/Virgin): Revert to previous links. * northamerica (Mont, America/Blanc-Sablon, America/Montreal) (America/Atikokan, America/Creston, America/Anguilla, America/Antigua) (Bahamas, America/Nassau, America/Cayman, America/Dominica) (America/Grenada, America/Guadeloupe, America/Montserrat) (America/St_Kitts, America/St_Lucia, America/St_Vincent) (America/Tortola, America/St_Thomas): * southamerica (America/Aruba, America/Curacao, America/Port_of_Spain): Restore these rules and zones. * .gitignore: Add back-pre1970. --- .gitignore | 1 - Makefile | 34 ++----- back-pre1970.awk | 18 ---- backward | 32 ++---- northamerica | 140 ++++++++++++++++++++------ pre1970 | 291 ------------------------------------------------------- southamerica | 20 +++- 7 files changed, 140 insertions(+), 396 deletions(-) delete mode 100644 back-pre1970.awk delete mode 100644 pre1970 diff --git a/.gitignore b/.gitignore index 28b1bc9..18dbbcc 100644 --- a/.gitignore +++ b/.gitignore @@ -4,7 +4,6 @@ *.txt *~ ChangeLog -back-pre1970 date leapseconds time.tab diff --git a/Makefile b/Makefile index ffddb08..e439055 100644 --- a/Makefile +++ b/Makefile @@ -49,22 +49,6 @@ POSIXRULES= America/New_York ZONETABTYPE= zone -# How to support obsolescent time zones in a backward-compatible way. -# This variable affects only pre-1970 time stamps, on hosts that support them. -# It has two possible values, 'backward' and 'pre1970 back-pre1970'. -# -# 'backward' is the traditional approach, and is simpler and more efficient; -# it is designed to generate one zone for each region where clocks have agreed -# since 1970. -# -# 'pre1970 back-pre1970' can generate more than one zone in that situation, -# which means it can preserve a bit of pre-1970 data that 'backward' does not; -# almost all pre-1970 data is missing, though, so don't get your hopes up. -# -# Sometimes 'backward' is more-compatible with earlier versions of this database, -# and sometimes 'pre1970 back-pre1970' is; it depends on the situation. -BACKWARD= backward - # Also see TZDEFRULESTRING below, which takes effect only # if the time zone files cannot be accessed. @@ -338,7 +322,7 @@ COMMON= Makefile DOCS= README Theory $(MANS) date.1 PRIMARY_YDATA= africa antarctica asia australasia \ europe northamerica southamerica -YDATA= $(PRIMARY_YDATA) pacificnew etcetera $(BACKWARD) +YDATA= $(PRIMARY_YDATA) pacificnew etcetera backward NDATA= systemv factory SDATA= solar87 solar88 solar89 TDATA= $(YDATA) $(NDATA) $(SDATA) @@ -346,10 +330,10 @@ TABDATA= iso3166.tab time.tab zone.tab DATA= $(YDATA) $(NDATA) $(SDATA) $(TABDATA) \ leap-seconds.list yearistype.sh WEB_PAGES= tz-art.htm tz-link.htm -AWK_SCRIPTS= back-pre1970.awk checktab.awk leapseconds.awk zone-time.awk +AWK_SCRIPTS= checktab.awk leapseconds.awk zone-time.awk MISC= usno1988 usno1989 usno1989a usno1995 usno1997 usno1998 \ - $(WEB_PAGES) $(AWK_SCRIPTS) \ - workman.sh zoneinfo2tdf.pl + $(WEB_PAGES) $(AWK_SCRIPTS) workman.sh \ + zoneinfo2tdf.pl ENCHILADA= $(COMMON) $(DOCS) $(SOURCES) $(DATA) $(MISC) # And for the benefit of csh users on systems that assume the user @@ -440,9 +424,6 @@ zones: $(REDO) time.tab: $(YDATA) zone.tab zone-time.awk $(AWK) -f zone-time.awk $(YDATA) >$@ -back-pre1970: pre1970 backward - $(AWK) -v pre1970=pre1970 -f $@.awk backward >$@ - $(TZLIB): $(LIBOBJS) -mkdir $(TOPDIR) $(LIBDIR) ar ru $@ $(LIBOBJS) @@ -477,7 +458,7 @@ check_web: $(WEB_PAGES) clean_misc: rm -f core *.o *.out \ - back-pre1970 time.tab \ + time.tab \ date leapseconds tzselect version.h zdump zic yearistype clean: clean_misc rm -f -r tzpublic @@ -509,7 +490,7 @@ set-timestamps: $$cmd || exit; \ done -# The zics below ensure that each non-pre1970 data file can stand on its own. +# The zics below ensure that each data file can stand on its own. # We also do an all-files run to catch links to links. check_public: $(ENCHILADA) @@ -517,8 +498,7 @@ check_public: $(ENCHILADA) make "CFLAGS=$(GCC_DEBUG_FLAGS)" mkdir tzpublic for i in $(TDATA) ; do \ - test $$i = pre1970 || $(zic) -v -d tzpublic $$i 2>&1 \ - || exit; \ + $(zic) -v -d tzpublic $$i 2>&1 || exit; \ done $(zic) -v -d tzpublic $(TDATA) rm -f -r tzpublic diff --git a/back-pre1970.awk b/back-pre1970.awk deleted file mode 100644 index f7c54fc..0000000 --- a/back-pre1970.awk +++ /dev/null @@ -1,18 +0,0 @@ -# Generate 'back-pre1970' from the two input files 'pre1970' and 'backward'. -# The output consists of all lines in 'backward' that are not links to -# files mentioned in 'pre1970'. Think of it as 'backward' minus 'pre1970'. - -# The 'backward' file is the input. -# The awk variable 'pre1970' contains the name of the pre1970 file. - -# This file is in the public domain. - -# Contributed by Paul Eggert. - -BEGIN { - while ((getline <pre1970) == 1) - if ($1 == "Zone") - pre1970_zone[$2] = 1 -} - -! (/^Link/ && pre1970_zone[$3]) { print } diff --git a/backward b/backward index efb5353..561e2ff 100644 --- a/backward +++ b/backward @@ -7,47 +7,27 @@ Link Africa/Asmara Africa/Asmera Link Africa/Bamako Africa/Timbuktu -Link America/Puerto_Rico America/Anguilla -Link America/Puerto_Rico America/Antigua Link America/Argentina/Catamarca America/Argentina/ComodRivadavia -Link America/Puerto_Rico America/Aruba -Link America/Panama America/Atikokan Link America/Adak America/Atka -Link America/Puerto_Rico America/Blanc-Sablon Link America/Argentina/Buenos_Aires America/Buenos_Aires Link America/Argentina/Catamarca America/Catamarca -Link America/Panama America/Cayman -Link America/Panama America/Coral_Harbour +Link America/Atikokan America/Coral_Harbour Link America/Argentina/Cordoba America/Cordoba -Link America/Phoenix America/Creston -Link America/Puerto_Rico America/Curacao -Link America/Puerto_Rico America/Dominica Link America/Tijuana America/Ensenada Link America/Indiana/Indianapolis America/Fort_Wayne -Link America/Puerto_Rico America/Grenada -Link America/Puerto_Rico America/Guadeloupe Link America/Indiana/Indianapolis America/Indianapolis Link America/Argentina/Jujuy America/Jujuy Link America/Indiana/Knox America/Knox_IN -Link America/Puerto_Rico America/Kralendijk +Link America/Curacao America/Kralendijk Link America/Kentucky/Louisville America/Louisville -Link America/Puerto_Rico America/Lower_Princes -Link America/Puerto_Rico America/Marigot +Link America/Curacao America/Lower_Princes +Link America/Guadeloupe America/Marigot Link America/Argentina/Mendoza America/Mendoza -Link America/Toronto America/Montreal -Link America/Puerto_Rico America/Montserrat -Link America/Toronto America/Nassau -Link America/Puerto_Rico America/Port_of_Spain Link America/Rio_Branco America/Porto_Acre Link America/Argentina/Cordoba America/Rosario Link America/Denver America/Shiprock -Link America/Puerto_Rico America/St_Barthelemy -Link America/Puerto_Rico America/St_Kitts -Link America/Puerto_Rico America/St_Lucia -Link America/Puerto_Rico America/St_Thomas -Link America/Puerto_Rico America/St_Vincent -Link America/Puerto_Rico America/Tortola -Link America/Puerto_Rico America/Virgin +Link America/Guadeloupe America/St_Barthelemy +Link America/St_Thomas America/Virgin Link Pacific/Auckland Antarctica/McMurdo Link Pacific/Auckland Antarctica/South_Pole Link Europe/Oslo Arctic/Longyearbyen diff --git a/northamerica b/northamerica index 6210318..418261f 100644 --- a/northamerica +++ b/northamerica @@ -1341,9 +1341,13 @@ Zone America/Moncton -4:19:08 - LMT 1883 Dec 9 # Quebec -# From Paul Eggert (2013-08-26): +# From Paul Eggert (2013-08-30): # Since 1970 most of Quebec has been like Toronto. -# See America/Toronto. +# However, because earlier versions of the tz database mistakenly relied on data +# from Shanks & Pottenger saying that Quebec differed from Ontario after 1970, +# a separate entry was created for most of Quebec. We're loath to lose +# its pre-1970 info, even though the tz database is normally limited to +# zones that differ after 1970, so keep this otherwise out-of-scope entry. # Matthews and Vincent (1998) also write that Quebec east of the -63 # meridian is supposed to observe AST, but residents as far east as @@ -1357,7 +1361,50 @@ Zone America/Moncton -4:19:08 - LMT 1883 Dec 9 # says this common practice was codified into law as of 2007. # For lack of better info, guess this practice began around 1970, contra to # Shanks & Pottenger who have this region observing AST/ADT. -# See America/Puerto_Rico. +# for post-1970 data America/Puerto_Rico. + +# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S +Rule Mont 1917 only - Mar 25 2:00 1:00 D +Rule Mont 1917 only - Apr 24 0:00 0 S +Rule Mont 1919 only - Mar 31 2:30 1:00 D +Rule Mont 1919 only - Oct 25 2:30 0 S +Rule Mont 1920 only - May 2 2:30 1:00 D +Rule Mont 1920 1922 - Oct Sun>=1 2:30 0 S +Rule Mont 1921 only - May 1 2:00 1:00 D +Rule Mont 1922 only - Apr 30 2:00 1:00 D +Rule Mont 1924 only - May 17 2:00 1:00 D +Rule Mont 1924 1926 - Sep lastSun 2:30 0 S +Rule Mont 1925 1926 - May Sun>=1 2:00 1:00 D +# The 1927-to-1937 rules can be expressed more simply as +# Rule Mont 1927 1937 - Apr lastSat 24:00 1:00 D +# Rule Mont 1927 1937 - Sep lastSat 24:00 0 S +# The rules below avoid use of 24:00 +# (which pre-1998 versions of zic cannot handle). +Rule Mont 1927 only - May 1 0:00 1:00 D +Rule Mont 1927 1932 - Sep lastSun 0:00 0 S +Rule Mont 1928 1931 - Apr lastSun 0:00 1:00 D +Rule Mont 1932 only - May 1 0:00 1:00 D +Rule Mont 1933 1940 - Apr lastSun 0:00 1:00 D +Rule Mont 1933 only - Oct 1 0:00 0 S +Rule Mont 1934 1939 - Sep lastSun 0:00 0 S +Rule Mont 1946 1973 - Apr lastSun 2:00 1:00 D +Rule Mont 1945 1948 - Sep lastSun 2:00 0 S +Rule Mont 1949 1950 - Oct lastSun 2:00 0 S +Rule Mont 1951 1956 - Sep lastSun 2:00 0 S +Rule Mont 1957 1973 - Oct lastSun 2:00 0 S + +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Blanc-Sablon -3:48:28 - LMT 1884 + -4:00 Canada A%sT 1970 + -4:00 - AST +Zone America/Montreal -4:54:16 - LMT 1884 + -5:00 Mont E%sT 1918 + -5:00 Canada E%sT 1919 + -5:00 Mont E%sT 1942 Feb 9 2:00s + -5:00 Canada E%sT 1946 + -5:00 Mont E%sT 1974 + -5:00 Canada E%sT + # Ontario @@ -1423,16 +1470,14 @@ Zone America/Moncton -4:19:08 - LMT 1883 Dec 9 # can say for certain that Atikokan has been practicing the current # time keeping since 1952, at least. -# From Paul Eggert (2013-08-26): +# From Paul Eggert (2006-07-17): # Shanks & Pottenger say that Atikokan has agreed with Rainy River # ever since standard time was introduced, but the information from # McKinnon sounds more authoritative. For now, assume that Atikokan # switched to EST immediately after WWII era daylight saving time # ended. This matches the old (less-populous) America/Coral_Harbour # entry since our cutoff date of 1970, so we can move -# America/Coral_Harbour to the 'backward' file. And Atikokan itself -# is the same as America/Panama since 1970, so we can move -# America/Atikokan to the 'backward' file as well. +# America/Coral_Harbour to the 'backward' file. # From Mark Brader (2010-03-06): # @@ -1590,6 +1635,11 @@ Zone America/Rainy_River -6:18:16 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 1:00 CDT 1942 Feb 9 2:00s -6:00 Canada C%sT +Zone America/Atikokan -6:06:28 - LMT 1895 + -6:00 Canada C%sT 1940 Sep 29 + -6:00 1:00 CDT 1942 Feb 9 2:00s + -6:00 Canada C%sT 1945 Sep 30 2:00 + -5:00 - EST # Manitoba @@ -1824,8 +1874,7 @@ Zone America/Edmonton -7:33:52 - LMT 1906 Sep # period should be PDT rather than MST, but that doesn't seem important enough # (to anyone) to further complicate the rules. -# From Paul Eggert (2013-08-26): -# See America/Phoenix, since Creston has agreed with Phoenix since 1970. +# The transition dates (and times) are guesses. # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule Vanc 1918 only - Apr 14 2:00 1:00 D @@ -1845,6 +1894,10 @@ Zone America/Dawson_Creek -8:00:56 - LMT 1884 -8:00 Canada P%sT 1947 -8:00 Vanc P%sT 1972 Aug 30 2:00 -7:00 - MST +Zone America/Creston -7:46:04 - LMT 1884 + -7:00 - MST 1916 Oct 1 + -8:00 - PST 1918 Jun 2 + -7:00 - MST # Northwest Territories, Nunavut, Yukon @@ -2495,10 +2548,15 @@ Zone America/Santa_Isabel -7:39:28 - LMT 1922 Jan 1 0:20:32 ############################################################################### # Anguilla -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Anguilla -4:12:16 - LMT 1912 Mar 2 + -4:00 - AST # Antigua and Barbuda -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Antigua -4:07:12 - LMT 1912 Mar 2 + -5:00 - EST 1951 + -4:00 - AST # Bahamas # @@ -2508,8 +2566,14 @@ Zone America/Santa_Isabel -7:39:28 - LMT 1922 Jan 1 0:20:32 # The Bahamas announced about a month ago that they plan to change their DST # rules to sync with the U.S. starting in 2007.... # http://www.jonesbahamas.com/?c=45&a=10412 -# -# See America/Toronto. + +# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S +Rule Bahamas 1964 1975 - Oct lastSun 2:00 0 S +Rule Bahamas 1964 1975 - Apr lastSun 2:00 1:00 D +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Nassau -5:09:30 - LMT 1912 Mar 2 + -5:00 Bahamas E%sT 1976 + -5:00 US E%sT # Barbados @@ -2559,7 +2623,10 @@ Zone Atlantic/Bermuda -4:19:18 - LMT 1930 Jan 1 2:00 # Hamilton -4:00 US A%sT # Cayman Is -# See America/Panama. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Cayman -5:25:32 - LMT 1890 # Georgetown + -5:07:12 - KMT 1912 Feb # Kingston Mean Time + -5:00 - EST # Costa Rica @@ -2805,7 +2872,9 @@ Zone America/Havana -5:29:28 - LMT 1890 -5:00 Cuba C%sT # Dominica -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Dominica -4:05:36 - LMT 1911 Jul 1 0:01 # Roseau + -4:00 - AST # Dominican Republic @@ -2854,10 +2923,15 @@ Zone America/El_Salvador -5:56:48 - LMT 1921 # San Salvador -6:00 Salv C%sT # Grenada -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Grenada -4:07:00 - LMT 1911 Jul # St George's + -4:00 - AST # Guadeloupe -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Guadeloupe -4:06:08 - LMT 1911 Jun 8 # Pointe a Pitre + -4:00 - AST +# Use America/Guadeloupe also for St Barthelemy and for St Martin (French part). # Guatemala # @@ -3027,7 +3101,9 @@ Zone America/Martinique -4:04:20 - LMT 1890 # Fort-de-France # From Paul Eggert (2006-03-22): # In 1995 volcanic eruptions forced evacuation of Plymouth, the capital. # world.gazetteer.com says Cork Hill is the most populous location now. -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Montserrat -4:08:52 - LMT 1911 Jul 1 0:01 # Cork Hill + -4:00 - AST # Nicaragua # @@ -3108,17 +3184,16 @@ Zone America/Puerto_Rico -4:24:25 - LMT 1899 Mar 28 12:00 # San Juan -4:00 US A%sT 1946 -4:00 - AST -# St Barthelemy -# See America/Puerto_Rico. - # St Kitts-Nevis -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/St_Kitts -4:10:52 - LMT 1912 Mar 2 # Basseterre + -4:00 - AST # St Lucia -# See America/Puerto_Rico. - -# St Martin (French part) -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/St_Lucia -4:04:00 - LMT 1890 # Castries + -4:04:00 - CMT 1912 # Castries Mean Time + -4:00 - AST # St Pierre and Miquelon # There are too many St Pierres elsewhere, so we'll use `Miquelon'. @@ -3129,7 +3204,10 @@ Zone America/Miquelon -3:44:40 - LMT 1911 May 15 # St Pierre -3:00 Canada PM%sT # St Vincent and the Grenadines -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/St_Vincent -4:04:56 - LMT 1890 # Kingstown + -4:04:56 - KMT 1912 # Kingstown Mean Time + -4:00 - AST # Turks and Caicos # @@ -3163,7 +3241,11 @@ Zone America/Grand_Turk -4:44:32 - LMT 1890 -5:00 TC E%sT # British Virgin Is -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Tortola -4:18:28 - LMT 1911 Jul # Road Town + -4:00 - AST # Virgin Is -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/St_Thomas -4:19:44 - LMT 1911 Jul # Charlotte Amalie + -4:00 - AST diff --git a/pre1970 b/pre1970 deleted file mode 100644 index d8b8f34..0000000 --- a/pre1970 +++ /dev/null @@ -1,291 +0,0 @@ -# Pre-1970 data - -# This file is in the public domain. - -# This file contains zones that were formerly in other source files, -# but were later removed or replaced by backward-compatibility links -# as they differ from other zones only in pre-1970 time stamps. - -# Although the tz database focuses on post-1970 time stamps, these -# entries are retained here as they may be of some use to people -# interested in pre-1970 time stamps, even though they cover only a -# tiny sliver of pre-1970 data and are unreliable for that data. -# Also, these entries can help with backward compatibility with some -# old versions of the tz database. They are incompatible with other -# old versions of the database, though; it depends on which old -# version you're interested in. - -# Entries are sorted by Zone name. Each entry is preceded by the name -# of the country that the entry is in, along with any other commentary -# and rules associated with the entry. Some rules, e.g., 'Canada', -# are defined by other source files; this file is not intended to be -# used without those other files. - -# Zone NAME GMTOFF RULES FORMAT [UNTIL] - -# Mali -# no longer different from Bamako, but too famous to omit -Zone Africa/Timbuktu -0:12:04 - LMT 1912 - 0:00 - GMT - -# Anguilla -Zone America/Anguilla -4:12:16 - LMT 1912 Mar 2 - -4:00 - AST - -# Antigua and Barbuda -Zone America/Antigua -4:07:12 - LMT 1912 Mar 2 - -5:00 - EST 1951 - -4:00 - AST - -# Argentina -# Chubut (CH) -# The name "Comodoro Rivadavia" exceeds the 14-byte POSIX limit. -Zone America/Argentina/ComodRivadavia -4:30:00 - LMT 1894 Oct 31 - -4:16:48 - CMT 1920 May - -4:00 - ART 1930 Dec - -4:00 Arg AR%sT 1969 Oct 5 - -3:00 Arg AR%sT 1991 Mar 3 - -4:00 - WART 1991 Oct 20 - -3:00 Arg AR%sT 1999 Oct 3 - -4:00 Arg AR%sT 2000 Mar 3 - -3:00 - ART 2004 Jun 1 - -4:00 - WART 2004 Jun 20 - -3:00 - ART - -# Aruba -Zone America/Aruba -4:40:24 - LMT 1912 Feb 12 # Oranjestad - -4:30 - ANT 1965 # Netherlands Antilles Time - -4:00 - AST - -# Canada - -Zone America/Atikokan -6:06:28 - LMT 1895 - -6:00 Canada C%sT 1940 Sep 29 - -6:00 1:00 CDT 1942 Feb 9 2:00s - -6:00 Canada C%sT 1945 Sep 30 2:00 - -5:00 - EST - -Zone America/Blanc-Sablon -3:48:28 - LMT 1884 - -4:00 Canada A%sT 1970 - -4:00 - AST - -# Cayman Is -Zone America/Cayman -5:25:32 - LMT 1890 # Georgetown - -5:07:12 - KMT 1912 Feb # Kingston Mean Time - -5:00 - EST - -# Canada -Zone America/Coral_Harbour -5:32:40 - LMT 1884 - -5:00 NT_YK E%sT 1946 - -5:00 - EST - -# Curacao -Zone America/Curacao -4:35:47 - LMT 1912 Feb 12 # Willemstad - -4:30 - ANT 1965 # Netherlands Antilles Time - -4:00 - AST - -# Dominica -Zone America/Dominica -4:05:36 - LMT 1911 Jul 1 0:01 # Roseau - -4:00 - AST - -# Mexico -Zone America/Ensenada -7:46:28 - LMT 1922 Jan 1 0:13:32 - -8:00 - PST 1927 Jun 10 23:00 - -7:00 - MST 1930 Nov 16 - -8:00 - PST 1942 Apr - -7:00 - MST 1949 Jan 14 - -8:00 - PST 1996 - -8:00 Mexico P%sT - -# US -Zone America/Fort_Wayne -5:00 US E%sT 1946 - -5:00 - EST # Always EST as of 1986 - -# Grenada -Zone America/Grenada -4:07:00 - LMT 1911 Jul # St George's - -4:00 - AST - -# Guadeloupe -Zone America/Guadeloupe -4:06:08 - LMT 1911 Jun 8 # Pointe a Pitre - -4:00 - AST - -# Canada -# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S -Rule Mont 1917 only - Mar 25 2:00 1:00 D -Rule Mont 1917 only - Apr 24 0:00 0 S -Rule Mont 1919 only - Mar 31 2:30 1:00 D -Rule Mont 1919 only - Oct 25 2:30 0 S -Rule Mont 1920 only - May 2 2:30 1:00 D -Rule Mont 1920 1922 - Oct Sun>=1 2:30 0 S -Rule Mont 1921 only - May 1 2:00 1:00 D -Rule Mont 1922 only - Apr 30 2:00 1:00 D -Rule Mont 1924 only - May 17 2:00 1:00 D -Rule Mont 1924 1926 - Sep lastSun 2:30 0 S -Rule Mont 1925 1926 - May Sun>=1 2:00 1:00 D -# The 1927-to-1937 rules can be expressed more simply as -# Rule Mont 1927 1937 - Apr lastSat 24:00 1:00 D -# Rule Mont 1927 1937 - Sep lastSat 24:00 0 S -# The rules below avoid use of 24:00 -# (which pre-1998 versions of zic cannot handle). -Rule Mont 1927 only - May 1 0:00 1:00 D -Rule Mont 1927 1932 - Sep lastSun 0:00 0 S -Rule Mont 1928 1931 - Apr lastSun 0:00 1:00 D -Rule Mont 1932 only - May 1 0:00 1:00 D -Rule Mont 1933 1940 - Apr lastSun 0:00 1:00 D -Rule Mont 1933 only - Oct 1 0:00 0 S -Rule Mont 1934 1939 - Sep lastSun 0:00 0 S -Rule Mont 1946 1973 - Apr lastSun 2:00 1:00 D -Rule Mont 1945 1948 - Sep lastSun 2:00 0 S -Rule Mont 1949 1950 - Oct lastSun 2:00 0 S -Rule Mont 1951 1956 - Sep lastSun 2:00 0 S -Rule Mont 1957 1973 - Oct lastSun 2:00 0 S -# Zone NAME GMTOFF RULES FORMAT [UNTIL] -Zone America/Montreal -4:54:16 - LMT 1884 - -5:00 Mont E%sT 1918 - -5:00 Canada E%sT 1919 - -5:00 Mont E%sT 1942 Feb 9 2:00s - -5:00 Canada E%sT 1946 - -5:00 Mont E%sT 1974 - -5:00 Canada E%sT - -# Montserrat -Zone America/Montserrat -4:08:52 - LMT 1911 Jul 1 0:01 # Cork Hill - -4:00 - AST - -# Bahamas -# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S -Rule Bahamas 1964 1975 - Oct lastSun 2:00 0 S -Rule Bahamas 1964 1975 - Apr lastSun 2:00 1:00 D -# Zone NAME GMTOFF RULES FORMAT [UNTIL] -Zone America/Nassau -5:09:30 - LMT 1912 Mar 2 - -5:00 Bahamas E%sT 1976 - -5:00 US E%sT - -# Trinidad and Tobago -Zone America/Port_of_Spain -4:06:04 - LMT 1912 Mar 2 - -4:00 - AST - -# Brazil -# Rio_Branco is too ambiguous, since there's a Rio Branco in Uruguay too. -Zone America/Porto_Acre -4:31:12 - LMT 1914 - -5:00 Brazil AC%sT 1988 Sep 12 - -5:00 - ACT - -# Argentina -# Santa Fe (SF), Entre Rios (ER), Corrientes (CN), Misiones (MN), Chaco (CC), -# Formosa (FM), La Pampa (LP), Chubut (CH) -Zone America/Rosario -4:02:40 - LMT 1894 Nov - -4:16:44 - CMT 1920 May - -4:00 - ART 1930 Dec - -4:00 Arg AR%sT 1969 Oct 5 - -3:00 Arg AR%sT 1991 Jul - -3:00 - ART 1999 Oct 3 0:00 - -4:00 Arg AR%sT 2000 Mar 3 0:00 - -3:00 - ART - -# St Kitts-Nevis -Zone America/St_Kitts -4:10:52 - LMT 1912 Mar 2 # Basseterre - -4:00 - AST - -# St Lucia -Zone America/St_Lucia -4:04:00 - LMT 1890 # Castries - -4:04:00 - CMT 1912 # Castries Mean Time - -4:00 - AST - -# Virgin Is -Zone America/St_Thomas -4:19:44 - LMT 1911 Jul # Charlotte Amalie - -4:00 - AST - -# St Vincent and the Grenadines -Zone America/St_Vincent -4:04:56 - LMT 1890 # Kingstown - -4:04:56 - KMT 1912 # Kingstown Mean Time - -4:00 - AST - -# British Virgin Is -Zone America/Tortola -4:18:28 - LMT 1911 Jul # Road Town - -4:00 - AST - -# McMurdo, Ross Island, since 1955-12 -Zone Antarctica/McMurdo 0 - zzz 1956 - 12:00 NZAQ NZ%sT - -# Japan -Zone Asia/Ishigaki 8:16:36 - LMT 1896 - 8:00 - CST - -# Israel -Zone Asia/Tel_Aviv 2:19:04 - LMT 1880 - 2:21 - JMT 1918 - 2:00 Zion I%sT - -# Russia -Zone Asia/Tomsk 5:39:52 - LMT 1924 May 2 - 6:00 - TSK 1957 Mar - 7:00 Russia TS%s 1991 Mar 31 2:00s - 6:00 1:00 TSD 1991 Sep 29 2:00s - 6:00 - TSK 1992 Jan 19 2:00s - 7:00 Russia TS%s - -# Svalbard & Jan Mayen -Zone Atlantic/Jan_Mayen -1:00 - EGT - -# Australia -Zone Australia/Canberra 9:56:32 - LMT 1895 Feb - 10:00 - EST 1917 Jan 1 0:01 - 10:00 Aus EST 1971 Oct 31 2:00 - 10:00 AN EST 1981 Oct 25 2:00 - 10:00 1:00 EST 1982 Apr 4 3:00 - 10:00 AN EST - -# UK -Zone Europe/Belfast -0:23:40 - LMT 1880 Aug 2 - -0:25:21 - DMT 1916 May 21 2:00 # Dublin/Dunsink MT - -0:25:21 1:00 IST 1916 Oct 1 2:00s # Irish Summer Time - 0:00 GB-Eire %s 1968 Oct 27 - 1:00 - BST 1971 Oct 31 2:00u - 0:00 GB-Eire %s 1996 - 0:00 EU GMT/BST - -# Slovenia -Zone Europe/Ljubljana 0:58:04 - LMT 1884 - 1:00 - CET 1941 Apr 18 23:00 - 1:00 C-Eur CE%sT 1945 May 8 2:00s - 1:00 1:00 CEST 1945 Sep 16 2:00s - 1:00 - CET 1982 Nov 27 - 1:00 EU CE%sT - -# Bosnia and Herzegovina -Zone Europe/Sarajevo 1:13:40 - LMT 1884 - 1:00 - CET 1941 Apr 18 23:00 - 1:00 C-Eur CE%sT 1945 May 8 2:00s - 1:00 1:00 CEST 1945 Sep 16 2:00s - 1:00 - CET 1982 Nov 27 - 1:00 EU CE%sT - -# Macedonia -Zone Europe/Skopje 1:25:44 - LMT 1884 - 1:00 - CET 1941 Apr 18 23:00 - 1:00 C-Eur CE%sT 1945 May 8 2:00s - 1:00 1:00 CEST 1945 Sep 16 2:00s - 1:00 - CET 1982 Nov 27 - 1:00 EU CE%sT - -# Moldova -Zone Europe/Tiraspol 1:58:32 - LMT 1880 - 1:55 - CMT 1918 Feb 15 # Chisinau MT - 1:44:24 - BMT 1931 Jul 24 # Bucharest MT - 2:00 Romania EE%sT 1940 Aug 15 - 2:00 1:00 EEST 1941 Jul 17 - 1:00 C-Eur CE%sT 1944 Aug 24 - 3:00 Russia MSK/MSD 1991 Mar 31 2:00 - 2:00 Russia EE%sT 1992 Jan 19 2:00 - 3:00 Russia MSK/MSD - -# Croatia -# Zone NAME GMTOFF RULES FORMAT [UNTIL] -Zone Europe/Zagreb 1:03:52 - LMT 1884 - 1:00 - CET 1941 Apr 18 23:00 - 1:00 C-Eur CE%sT 1945 May 8 2:00s - 1:00 1:00 CEST 1945 Sep 16 2:00s - 1:00 - CET 1982 Nov 27 - 1:00 EU CE%sT diff --git a/southamerica b/southamerica index 59f5fe7..ff47cef 100644 --- a/southamerica +++ b/southamerica @@ -631,7 +631,10 @@ Zone America/Argentina/Ushuaia -4:33:12 - LMT 1894 Oct 31 -3:00 - ART # Aruba -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Aruba -4:40:24 - LMT 1912 Feb 12 # Oranjestad + -4:30 - ANT 1965 # Netherlands Antilles Time + -4:00 - AST # Bolivia # Zone NAME GMTOFF RULES FORMAT [UNTIL] @@ -1325,7 +1328,7 @@ Zone America/Bogota -4:56:16 - LMT 1884 Mar 13 # Curacao -# Milne gives 4:35:46.9 for Curacao mean time. +# Milne gives 4:35:46.9 for Curacao mean time; round to nearest. # # From Paul Eggert (2006-03-22): # Shanks & Pottenger say that The Bottom and Philipsburg have been at @@ -1341,7 +1344,14 @@ Zone America/Bogota -4:56:16 - LMT 1884 Mar 13 # Netherlands as Kingdom Islands. This won't affect their time zones # though, as far as we know. # -# For all these regions, see America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Curacao -4:35:47 - LMT 1912 Feb 12 # Willemstad + -4:30 - ANT 1965 # Netherlands Antilles Time + -4:00 - AST + +# Sint Maarten +# Caribbean Netherlands +# Use America/Curacao. # Ecuador # @@ -1615,7 +1625,9 @@ Zone America/Paramaribo -3:40:40 - LMT 1911 -3:00 - SRT # Trinidad and Tobago -# See America/Puerto_Rico. +# Zone NAME GMTOFF RULES FORMAT [UNTIL] +Zone America/Port_of_Spain -4:06:04 - LMT 1912 Mar 2 + -4:00 - AST # Uruguay # From Paul Eggert (1993-11-18): -- 1.8.1.2

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winnowing stats
by Zefram Sept. 3, 2013

Sept. 3, 2013

Here are some stats on how much difference winnowing makes to the dataset. Baseline: the source files define 441 distinct zones. Winnowing then reduces the number of distinct zones thus: YEAR COUNT 0000 440 1880 440 1890 439 1900 439 1910 437 1920 435 1930 435 1940 434 1950 425 1960 423 1970 417 1980 391 1990 365 2000 339 2010 313 2020 305 The reduction by one zone for a threshold year of 0000 comes from Pacific/Johnston, a US minor outlying island, which is defined with data identical to the "HST" zone. (Contrary to the usual practice of using LMT for the first segment of geographical zones.) As the two tzfiles are byte-for-byte identical, tzwinnow will merge them regardless of date thresholds. The results for a threshold in the future set a lower limit on the size to which the database can be reduced by this mechanism. Relative to the present full database of 441 zones, it's only a modest gain. Using a threshold later than 1970 for installation purposes will probably only be attractive in a few more decades' time, when there have been many more zone splits arising from contemporary activity. A threshold later than 1970 is currently much more valuable for tzselect purposes. Here it's saving human cognitive load rather than storage space. The reduction in the number of zones is concentrated disproportionately in the countries that have the greatest complexity. This is particularly noticeable with the US zones, the list of which is quite unwieldy in unwinnowed form. Over the period where we attempt complete coverage (1970 to today), the rate at which the number of distinct zones changes is amazingly consistent at 26 per decade. A similar pattern emerges when winnowing with a varying upper date limit, showing that there's a long-term roughly constant rate of zone churn. The number of zones distinct within a single decade is also roughly constant, around 330. The number distinct within a single year hovers around 300, possibly showing a slight rising trend, but I suspect that's an artifact of incomplete data. This suggests that a strategy of winnowing with a moving threshold that remains N years ago will produce a roughly constant zone count. By contrast, the number of zones differing at any time post-1970 (currently 417), or from any other fixed threshold, can grow without bound, and it looks like it will. -zefram

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scope of tz database, scholarship
by Steve Allen Sept. 2, 2013

Sept. 2, 2013

For the sake of the scholarship I would like to see a modification of the current text that reads As for leap seconds, we don't know the history of earth's rotation accurately enough to map SI seconds to historical solar time to more than about one-hour accuracy; see Stephenson FR (2003), Historical eclipses and Earth's rotation, A&G 44: 2.22-2.27 <http://dx.doi.org/10.1046/j.1468-4004.2003.44222.x>. A more complete reference to the accuracy of historical Delta T is in Historical values of the Earth's clock error Delta T and the calculation of eclipses Morrison, L. V. & Stephenson, F. R. Journal for the History of Astronomy (ISSN 0021-8286), Vol. 35, Part 3, No. 120, p. 327 - 336 (2004) as can be seen at http://articles.adsabs.harvard.edu/full/2004JHA....35..327M where, in particular, Table 1 gives uncertainty estimates back nearly 3000 years. For the oldest data there is an addendum Addendum: Historical values of the Earth's clock error Morrison, L. V. & Stephenson, F. R. Journal for the History of Astronomy (ISSN 0021-8286), Vol. 36, Part 3, No. 124, p. 339 (2005) http://adsabs.harvard.edu/full/2005JHA....36..339M In addition to that, for all practical purposes, civil time prior to 1972 did not use SI seconds, but rather mean solar seconds, and for dates prior to 1955 there cannot even be an argument. Therefore in the extended range of the tz database there is an arguably unspecified point when the kind of seconds counted changes from mean solar (UT) to atomic (SI). -- Steve Allen <sla(a)ucolick.org> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m

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