Southern Vietnam: time zone history, and your birth hour
The clocks in Southern Vietnam have changed 8 times since 1900. Today they run on UTC+7; the last change was on 12 Jun 1975. A calculator that uses today’s offset for every birth is out by some minutes for anyone born in any of the different eras below.
Since 1925, the widest gap is the wartime, on Tokyo time from 1945: 120 minutes, enough to move nearly all of births into a different two-hour period.
Every era
| From – to | Clock | Versus today · births in another hour |
|---|---|---|
| 1 Jan 1900 – 30 Apr 1911 | UTC+7:07 local mean time | +7 min about 6% |
| 30 Apr 1911 – 1 Jan 1943 | UTC+7 standard time | same |
| 1 Jan 1943 – 15 Mar 1945 | UTC+8 standard time | +60 min about 50% |
| 15 Mar 1945 – 1 Sep 1945 | UTC+9 wartime, on Tokyo time | +120 min nearly all |
| 1 Sep 1945 – 1 Apr 1947 | UTC+7 standard time | same |
| 1 Apr 1947 – 1 Jul 1955 | UTC+8 standard time | +60 min about 50% |
| 1 Jul 1955 – 1 Jan 1960 | UTC+7 standard time | same |
| 1 Jan 1960 – 12 Jun 1975 | UTC+8 standard time | +60 min about 50% |
| 12 Jun 1975 – today | UTC+7 standard time | same |
The second figure in each row is the births moved into another two-hour period: about m/120 of them when the clock is m minutes out. For Kuala Lumpur, 30 minutes out from 1946 to 1981, the measured share is 26.0% of 4,000 sampled births.