[tz] uniform time in Switzerland in second half of 19th century

[Paul Eggert]

Thanks again.  I've pushed the following patch to the
experimental repository.

>From 09f994d25d62ba6027722fb873b0207f37bf496f Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert at cs.ucla.edu>
Date: Wed, 11 Sep 2013 09:17:03 -0700
Subject: [PATCH] * europe, zic.8: Correct Bern Mean Time to 0:29:46.

Reported by Alois Treindl in
<http://mm.icann.org/pipermail/tz/2013-September/020139.html>.
---
 europe | 22 +++++++++++++---------
 zic.8  | 17 ++++++++++-------
 2 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/europe b/europe
index 79376b8..8d26b4e 100644
--- a/europe
+++ b/europe
@@ -2650,32 +2650,36 @@ Zone Europe/Stockholm	1:12:12 -	LMT	1879 Jan  1
 # The 1940 rules must be deleted.
 #
 # One further detail for Switzerland, which is probably out of scope for
-# most users of tzdata:
-# The zone file
-# Zone    Europe/Zurich   0:34:08 -       LMT     1848 Sep 12
-#                          0:29:44 -       BMT     1894 Jun #Bern Mean Time
-#                          1:00    Swiss   CE%sT   1981
-#                          1:00    EU      CE%sT
+# most users of tzdata: The [Europe/Zurich zone] ...
 # describes all of Switzerland correctly, with the exception of
 # the Cantone Geneve (Geneva, Genf). Between 1848 and 1894 Geneve did not
 # follow Bern Mean Time but kept its own local mean time.
 # To represent this, an extra zone would be needed.
+#
+# From Alois Treindl (2013-09-11):
+# The Federal regulations say
+# http://www.admin.ch/opc/de/classified-compilation/20071096/index.html
+# ... the meridian for Bern mean time ... is 7 degrees 26'22.50".
+# Expressed in time, it is 0h29m45.5s.
 
-# From Paul Eggert (2013-09-09):
+# From Paul Eggert (2013-09-11):
+# Round to the nearest even second, 0:29:46.
+#
 # We can find no reliable source for Shanks's claim that all of Switzerland
 # except Geneva switched to Bern Mean Time at 00:00 on 1848-09-12.  On the
 # contrary, a more-reliable source talks about "the gradual introduction of a
 # national time (from the 1850s)" (Google translation) with a switch to CET in
 # 1894; see Speich's review of Messerli's thesis, Traverse 1997/3, 131-3
 # <http://www.tg.ethz.ch/dokumente/pdf_files/rez_messerli.pdf>.  For now, model
-# this messy process as a transition in 1855.  The "0:29:44" is also suspect.
+# this messy process as a transition in 1855.  Shanks's 1894 transition is more
+# plausible for Zurich but has not been checked.
 
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
 Rule	Swiss	1941	1942	-	May	Mon>=1	1:00	1:00	S
 Rule	Swiss	1941	1942	-	Oct	Mon>=1	2:00	0	-
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone	Europe/Zurich	0:34:08 -	LMT	1855 # See above comment.
-			0:29:44	-	BMT	1894 Jun # Bern Mean Time
+			0:29:46	-	BMT	1894 Jun # Bern Mean Time
 			1:00	Swiss	CE%sT	1981
 			1:00	EU	CE%sT
 
diff --git a/zic.8 b/zic.8
index b61ebd3..a2374a1 100644
--- a/zic.8
+++ b/zic.8
@@ -466,10 +466,10 @@ Rule	EU	1979	1995	-	Sep	lastSun	1:00u	0	-
 Rule	EU	1981	max	-	Mar	lastSun	1:00u	1:00	S
 Rule	EU	1996	max	-	Oct	lastSun	1:00u	0	-
 .sp
-.ta \w'# Zone\0\0'u +\w'Europe/Zurich\0\0'u +\w'0:34:08\0\0'u +\w'RULES/SAVE\0\0'u +\w'FORMAT\0\0'u
-# Zone	NAME	GMTOFF	RULES	FORMAT	UNTIL
+.ta \w'# Zone\0\0'u +\w'Europe/Zurich\0\0'u +\w'GMTOFF\0\0'u +\w'RULES/SAVE\0\0'u +\w'FORMAT\0\0'u
+# Zone	NAME	GMTOFF	RULES/SAVE	FORMAT	UNTIL
 Zone	Europe/Zurich	0:34:08	-	LMT	1855
-		0:29:44	-	BMT	1894 Jun
+		0:29:46	-	BMT	1894 Jun
 		1:00	Swiss	CE%sT	1981
 		1:00	EU	CE%sT
 .sp
@@ -478,10 +478,13 @@ Link	Europe/Zurich	Switzerland
 .in
 .fi
 In this example, the zone is named Europe/Zurich but it has an alias
-as Switzerland.  Zurich was 34 minutes and 8 seconds west of GMT until
-1855-01-01 at 00:00, when the offset changed to 29 minutes and 44
-seconds.  After 1894-06-01 at 00:00 Swiss daylight saving rules (defined
-with lines beginning with "Rule Swiss") apply, and the GMT offset
+
+as Switzerland.  This example says that Zurich was 34 minutes and 8
+seconds west of UT until 1855-01-01 at 00:00, when the legal offset
+was changed to 7\(de\|26\(fm\|22.50\(sd; although this works out to
+0:29.45.50, the input format cannot represent fractional seconds so it
+is rounded here.  After 1894-06-01 at 00:00 Swiss daylight saving rules
+(defined with lines beginning with "Rule Swiss") apply, and the UT offset
 became one hour.  From 1981 to the present, EU daylight saving rules have
 applied, and the UTC offset has remained at one hour.
 .PP
-- 
1.8.1.2