
Hi there - I've been lurking on the list for a while. I don't contribute much as a I'm a (humbly grateful) user of tz information, rather than a provider. I mentioned our http://permatime.com site, a while back, but don't think I explicitly asked for it to go on the twinsun link page under "Web pages using recent versions of the tz database". Can it? http://permatime.com is a service for generating and viewing links that refer to a particular point in time and can be displayed in multiple timezones. It uses the ruby tzinfo gem, based on the Olson Tz database. kind regards Tim http://permatime.com http://teamportfolios.com/permatime Tim Diggins http://red56.co.uk http://tim.teamportfolios.com/

tzdata gives for Vietnam timezone # From Shanks & Pottenger: # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Asia/Ho_Chi_Minh 7:06:40 - LMT 1906 Jun 9 7:06:20 - SMT 1911 Mar 11 0:01 # Saigon MT? 7:00 - ICT 1912 May 8:00 - ICT 1931 May 7:00 - ICT This is possibly wrong for the years beween 1911 and 1976. I am us9ing the source Gabriel, Traite de l'heure dans le monde, edition 1991. It deals with Vietnam under the entry 'Indochine Française' until 1954, and then separately with North and South Vietnam, until the unification in 1976. Gabriel gives this timezone information: French Indochina (including Vietnam, Cambodia, Laos) until 1 July 1906: local mean time until 1 May 1911: 7h6m44s east (meridian of Saigon) until 1 Jan 1943: 7h east from 1 Jan 1943: 8h east (with Daylight saving time, i.e. 9h east, between 14 March and 1 Sept 1945) North Vietnam until 15 April 1955: 8h east until 1 Jan 1960: 7h east until 1976 : 8h east For 1976, Gabriel does not give a transition date. The official reunification was on 2 July 1976. since 1976: 7h east South Vietnam: until 1976 (for date, see above): 8h east since 1976: 7h east I have searched for corroboration of the fact that Vietnam was on GMT + 8h in years when tzdata and Shanks claim 7h. For siginificant timed events during the Vietnam war, there must be newspaper reports which give local Vietnam time and corresponding US time. One such report I have found is the last helicopter out of Saigon, according to TIME magazine. http://www.time.com/time/magazine/article/0,9171,917411-2,00.html It says: Finally, at 5 p.m. Washington tune—it was then 5 a.m. in Saigon—Kissinger told the President that Martin was closing down the embassy and destroying its communications equipment. Minutes later, a helicopter broadcast the message: "Lady Ace Zero Nine, Code Two is aboard." Lady Ace 09 was the chopper's own call signal; Code Two designates an ambassador. This is 5 PM on 29 Paril 1975. Washington DC was on DST, i.e. on 4h west timezone. Universal time is 21:00 (09 pm). In Vietnam it is already the 30th of April, 5 am, in the morning. This means that Vietnam was 8 hours ahead of Universal time! This means that, at least for April 1975, the source Gabriel is right and Shanks and tzdata are wrong, because they claim 7h east. Conclusion: it is evident that Vietnam timezone history needs corrections, also in tzdata, because it should be correct at least starting from 1970. I would be reluctant to simply copy the Gabriel source, as it fails to give a transition date in 1976. But research is needed. The best would be local Newspaper archives in Saigon or Hanoi, if such exist. -- || Alois Treindl, Astrodienst AG, mailto:alois@astro.com || Zollikon/Zurich, Switzerland || Free astrological charts at http://www.astro.com/ || SWISS EPHEMERIS Free Edition at http://www.astro.com/swisseph/

I have found another source indicating that Vietnam was on UTC+8h in early April 1969, and not on UTC+7h as current tzdata claims. The source is a personal war memoir, http://www.military.com/Content/MoreContent?file=fowler01 The author writes in the second paragraph (refering to his trip to Vietnam around April 10, 1969): ----- quote There is a 14 hour time difference between South Vietnam and Central Standard Time here in the United States. ----- end quote Again, this is consistent with Vietnam being on 8h east at that time. Central Standard Time is 6h west, making the difference 14 hours.

It seems necessary to split North Vietnam and South Vietnam into two zones for timezone history between 1967 and 1975/1976 I have found corroboration that North Vietnam went from UTC+8 to UTC+7 on August 8, 1967, while South Vietnam stayed on UTC+8 'until after the end of the Vietnam war'. Saigon fell end of April 1975. Source: http://en.wikipedia.org/wiki/T%E1%BA%BFt There is another reference, discussing the difference between North and South Vietnam timezone in 1968, http://www.math.nus.edu.sg/aslaksen/calendar/cal.pdf on page 29. The timezone difference led to a different date for the Tet festival in that year, creating confusion about the starting data for the Vietcong's Tet offensive.
participants (2)
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Alois Treindl
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Tim Diggins