[tz] [PATCH] Revert recent pre-1970 changes.

Paul Eggert eggert at cs.ucla.edu
Sat Aug 31 10:00:30 UTC 2013

Stephen Colebourne wrote:
> it is hard to
> tell which changes are in and which are out.

That's easily accomplished by doing a git diff between
the last version before the controversial changes and
what's in there now.  Here's the output of
'git diff 81be53c16b97ce0bc561ce3891ce2503227e3369'.
As far as I can tell, none of the changes should affect
any of the time stamps, but of course it'd be nice if
you can confirm that with your testing.

diff --git a/Makefile b/Makefile
index a74d1a7..e439055 100644
--- a/Makefile
+++ b/Makefile
@@ -330,8 +330,9 @@ TABDATA=	iso3166.tab time.tab zone.tab
 			leap-seconds.list yearistype.sh
 WEB_PAGES=	tz-art.htm tz-link.htm
+AWK_SCRIPTS=	checktab.awk leapseconds.awk zone-time.awk
 MISC=		usno1988 usno1989 usno1989a usno1995 usno1997 usno1998 \
-			$(WEB_PAGES) checktab.awk leapseconds.awk workman.sh \
+			$(WEB_PAGES) $(AWK_SCRIPTS) workman.sh \
@@ -457,6 +458,7 @@ check_web:	$(WEB_PAGES)
 		rm -f core *.o *.out \
+		  time.tab \
 		  date leapseconds tzselect version.h zdump zic yearistype
 clean:		clean_misc
 		rm -f -r tzpublic
diff --git a/Theory b/Theory
index b4bd4c2..580b548 100644
--- a/Theory
+++ b/Theory
@@ -224,7 +224,23 @@ could misbehave if data were omitted for pre-1970 transitions.
 However, the database is not designed for and does not suffice for
 applications requiring accurate handling of all past times everywhere,
 as it would take far too much effort and guesswork to record all
-details of pre-1970 civil timekeeping.
+details of pre-1970 civil timekeeping.  The pre-1970 data in this
+database covers only a tiny sliver of how clocks actually behaved;
+the vast majority of the necessary information was lost or never
+recorded, and much of what little remains is fabricated.
+Local mean time (LMT) offsets are recorded in the database only
+because the format requires an offset.  They should not be considered
+meaningful, and should not prompt creation of zones merely because two
+locations differ in LMT.  Historically, not only did different
+locations in the same zone typically use different LMT offsets, often
+different people in the same location maintained mean-time clocks that
+differed significantly, and many people used solar or some other time
+instead of mean time.  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
 As noted in the README file, the tz database is not authoritative
 (particularly not for pre-1970 time stamps), and it surely has errors.
@@ -384,8 +400,11 @@ in decreasing order of importance:
 			name identifying each zone and append 'T', 'ST', etc.
 			as before; e.g. 'VLAST' for VLAdivostok Summer Time.
-	Use UTC (with time zone abbreviation "zzz") for locations while
-		uninhabited.  The "zzz" mnemonic is that these locations are,
+	Use 'LMT' for local mean time of locations before the introduction
+		of standard time; see "Scope of the tz database".
+	Use UTC (with time zone abbreviation 'zzz') for locations while
+		uninhabited.  The 'zzz' mnemonic is that these locations are,
 		in some sense, asleep.
 Application writers should note that these abbreviations are ambiguous
diff --git a/iso3166.tab b/iso3166.tab
index d9dcf6a..a1e4b42 100644
--- a/iso3166.tab
+++ b/iso3166.tab
@@ -53,7 +53,7 @@ BL	St Barthelemy
 BM	Bermuda
 BN	Brunei
 BO	Bolivia
-BQ	Bonaire, St Eustatius & Saba
+BQ	Caribbean Netherlands
 BR	Brazil
 BS	Bahamas
 BT	Bhutan
diff --git a/northamerica b/northamerica
index 7676c77..418261f 100644
--- a/northamerica
+++ b/northamerica
@@ -1341,25 +1341,27 @@ Zone America/Moncton	-4:19:08 -	LMT	1883 Dec  9
 # Quebec
-# From Paul Eggert (2006-07-09):
-# Shanks & Pottenger write that since 1970 most of Quebec has been
-# like Montreal.
+# From Paul Eggert (2013-08-30):
+# Since 1970 most of Quebec has been like 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.
-# From Paul Eggert (2006-06-27):
 # Matthews and Vincent (1998) also write that Quebec east of the -63
 # meridian is supposed to observe AST, but residents as far east as
 # Natashquan use EST/EDT, and residents east of Natashquan use AST.
-# In "Official time in Quebec" the Quebec department of justice writes in
-# http://www.justice.gouv.qc.ca/english/publications/generale/temps-regl-1-a.htm
-# that "The residents of the Municipality of the
-# Cote-Nord-du-Golfe-Saint-Laurent and the municipalities of Saint-Augustin,
-# Bonne-Esperance and Blanc-Sablon apply the Official Time Act as it is
-# written and use Atlantic standard time all year round. The same applies to
-# the residents of the Native facilities along the lower North Shore."
-# <http://www.assnat.qc.ca/eng/37legislature2/Projets-loi/Publics/06-a002.htm>
+# The Quebec department of justice writes in
+# "The situation in Minganie and Basse-Cote-Nord"
+# http://www.justice.gouv.qc.ca/english/publications/generale/temps-minganie-a.htm
+# that the coastal strip from just east of Natashquan to Blanc-Sablon
+# observes Atlantic standard time all year round.
+# http://www.assnat.qc.ca/Media/Process.aspx?MediaId=ANQ.Vigie.Bll.DocumentGenerique_8845en
 # 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.
+# for post-1970 data America/Puerto_Rico.
 Rule	Mont	1917	only	-	Mar	25	2:00	1:00	D
@@ -1622,7 +1624,7 @@ Zone America/Thunder_Bay -5:57:00 -	LMT	1895
 			-6:00	-	CST	1910
 			-5:00	-	EST	1942
 			-5:00	Canada	E%sT	1970
-			-5:00	Mont	E%sT	1973
+			-5:00	Toronto	E%sT	1973
 			-5:00	-	EST	1974
 			-5:00	Canada	E%sT
 Zone America/Nipigon	-5:53:04 -	LMT	1895
@@ -2617,7 +2619,7 @@ Zone	America/Belize	-5:52:48 -	LMT	1912 Apr
 Zone Atlantic/Bermuda	-4:19:18 -	LMT	1930 Jan  1 2:00    # Hamilton
 			-4:00	-	AST	1974 Apr 28 2:00
-			-4:00	Bahamas	A%sT	1976
+			-4:00	Canada	A%sT	1976
 			-4:00	US	A%sT
 # Cayman Is
diff --git a/southamerica b/southamerica
index 17150a8..ff47cef 100644
--- a/southamerica
+++ b/southamerica
@@ -1350,7 +1350,7 @@ Zone	America/Curacao	-4:35:47 -	LMT	1912 Feb 12	# Willemstad
 			-4:00	-	AST
 # Sint Maarten
-# Bonaire, Sint Estatius and Saba
+# Caribbean Netherlands
 # Use America/Curacao.
 # Ecuador
diff --git a/zone.tab b/zone.tab
index b4407f1..769432b 100644
--- a/zone.tab
+++ b/zone.tab
@@ -122,8 +122,7 @@ CA	+4612-05957	America/Glace_Bay	Atlantic Time - Nova Scotia - places that did n
 CA	+4606-06447	America/Moncton	Atlantic Time - New Brunswick
 CA	+5320-06025	America/Goose_Bay	Atlantic Time - Labrador - most locations
 CA	+5125-05707	America/Blanc-Sablon	Atlantic Standard Time - Quebec - Lower North Shore
-CA	+4531-07334	America/Montreal	Eastern Time - Quebec - most locations
-CA	+4339-07923	America/Toronto	Eastern Time - Ontario - most locations
+CA	+4339-07923	America/Toronto	Eastern Time - Ontario & Quebec - most locations
 CA	+4901-08816	America/Nipigon	Eastern Time - Ontario & Quebec - places that did not observe DST 1967-1973
 CA	+4823-08915	America/Thunder_Bay	Eastern Time - Thunder Bay, Ontario
 CA	+6344-06828	America/Iqaluit	Eastern Time - east Nunavut - most locations

More information about the tz mailing list