1948-1951 Asia/Tokyo DST information
It seems like the current info about past DST for Asia/Tokyo in tz database is incorrect. The law cited in the latest commit do say the DST en at 00:00 on the day after the second Saturday in September, however the second line of the law write that "the Second Saturday in September would have 25 hours in a day". I was made aware of it by reading an interview on NICT (The National Institute of Information and Communications Technology) of Japan and the history of DST in Japan given in the interview by NICT representative do said DST used to end at 25:00 there. See https://www.bengo4.com/internet/n_8461/
Phake Nick wrote:
The law cited in the latest commit do say the DST en at 00:00 on the day after the second Saturday in September, however the second line of the law write that "the Second Saturday in September would have 25 hours in a day".
Those mean the same thing. Since DST ends at 00:00 the day after Saturday, the clock jumps back from 24:00 on Saturday to 23:00 on Saturday, and Saturday has 25 hours.
Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change. 2018-09-08 15:36 "Paul Eggert" <eggert@cs.ucla.edu> wrote: Phake Nick wrote:
The law cited in the latest commit do say the DST en at 00:00 on the day after the second Saturday in September, however the second line of the law write that "the Second Saturday in September would have 25 hours in a day".
Those mean the same thing. Since DST ends at 00:00 the day after Saturday, the clock jumps back from 24:00 on Saturday to 23:00 on Saturday, and Saturday has 25 hours.
Phake Nick wrote:
Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Sorry, but that reading doesn't sound plausible to me. I can't imagine a law intending to refer to 24:59.9999... on Sunday (i.e., 00:59.9999.... on Monday) talking about the transition occurring the day after Saturday. But perhaps someone can dig up a newspaper in the affected area that explains things clearly to the general populace.
On 8 Sep 2018, at 17:55, Paul Eggert <eggert@cs.ucla.edu> wrote:
Phake Nick wrote:
Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Sorry, but that reading doesn't sound plausible to me. I can't imagine a law intending to refer to 24:59.9999... on Sunday (i.e., 00:59.9999.... on Monday) talking about the transition occurring the day after Saturday. But perhaps someone can dig up a newspaper in the affected area that explains things clearly to the general populace.
The question is whether the change is from 00:00 Sunday (IE 24:00 Saturday) to 23:00 Saturday or from 01:00 Sunday to 00:00 Sunday (IE 24:00 Saturday), isn't it? Or are 24 hours after these two cases—with "Saturday" replaced by "Sunday" and "Sunday" replaced by "Monday"—also possibilities? Which Sunday it is is not in dispute, is it?
Not really, it sat 25:00:00 at Saturday would become 00:00:00 on Sunday It used the tine from Saturday to refer to transition that occur at Sunday 00:00. Note: I realized there is a typo in my original message. Please check the corrected text in the quoted part. 2018-09-08 15:55, Paul Eggert <eggert@cs.ucla.edu> wrote:
Phake Nick wrote:
Not really. It would mean the Saturday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Sorry, but that reading doesn't sound plausible to me. I can't imagine a law intending to refer to 24:59.9999... on Sunday (i.e., 00:59.9999.... on Monday) talking about the transition occurring the day after Saturday. But perhaps someone can dig up a newspaper in the affected area that explains things clearly to the general populace.
Phake Nick wrote:
Not really, it sat 25:00:00 at Saturday would become 00:00:00 on Sunday It used the tine from Saturday to refer to transition that occur at Sunday 00:00.
The cited Japanese law <http://www.shugiin.go.jp/internet/itdb_housei.nsf/html/houritsu/002194804280...> says, "第二条 四月の第一土曜日の翌日（日曜日）は二十三時間をもつて一日とし、九月の第二土曜日は二十五時間をもつて一日とする", which Google translates as "Article 2. The day following the first Saturday of April (Sunday) shall be one day with twenty-three hours and the second Saturday of September shall be twenty-five hours a day." This law is compatible with what tzdb specifies, which is that the clock jumps back from 24:00 to 23:00 on Saturday, which means Saturday indeed has 25 hours, the last of which has timestamps duplicated from the next-to-last. As I understand it, you're saying that the practice in Japan (not specified in the law) was to call these timestamps 24:00 through 24:59 instead. A nice property of this practice would be that timestamps would not be ambiguous. During the period in question (1948-1951) it's unlikely that many physical clocks showed the times 24:00 through 24:59, so the question is whether people adjusted their 12-hour clocks from 1 o'clock (representing 25:00 Saturday) to 12 o'clock (representing 00:00 Sunday), or from 12 o'clock (representing 24:00 Saturday) to 11 o'clock (representing 23:00 Saturday). Both actions are consistent with the cited law, and so far we have no evidence what people actually did. Since tzdb cannot implement what you're suggesting, the answer to this question won't affect what we put into tzdb proper, though of course it should affect the commentary. One other thing. If your suggestion is that the practice was to simply number the timestamps in a day from 00:00 to the end of the day regardless of the day's length, then for consistency the timestamps in a spring-forward Sunday (i.e., the Sunday after a spring-forward transition) should have been 00:00 through 22:59. That is, in spring people in Japan would have moved their 12-hour clocks from 11 o'clock to 12 o'clock at 23:00 Sunday. I'm skeptical that this occurred, as it's typical to make the change Sunday morning in order to minimize disruption to the workweek starting Monday, so it's far more likely that people would have moved their clocks from 12 o'clock to 1 o'clock at 00:00 Sunday, as tzdb has it now. Surely a "just number the timestamps in a day consecutively" rule cannot be what was used in Japan; if there was a rule about 24:00 through 24:59 it was a special-case rule that appled only to fall-back Saturdays.
I can't speak to the interpretation of the law, but in Japan it's not uncommon to see the hours of a bar or restaurant listed as 17:00-25:00 or 12:00-26:00 or something like that. No idea if it would be used in this context or if the convention goes all the way back to the 40s, though. On September 8, 2018 7:55:37 AM UTC, Paul Eggert <eggert@cs.ucla.edu> wrote:
Phake Nick wrote:
Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Sorry, but that reading doesn't sound plausible to me. I can't imagine a law intending to refer to 24:59.9999... on Sunday (i.e., 00:59.9999.... on Monday) talking about the transition occurring the day after Saturday. But perhaps someone can dig up a newspaper in the affected area that explains things clearly to the general populace.
On 2018-09-08 01:50, Phake Nick wrote:
2018-09-08 15:36 "Paul Eggert" wrote:
On 2018-09-08 01:17, Phake Nick wrote:
The law cited in the latest commit do say the DST en at 00:00 on the day after the second Saturday in September, however the second line of the law write that "the Second Saturday in September would have 25 hours in a day". Those mean the same thing. Since DST ends at 00:00 the day after Saturday, the clock jumps back from 24:00 on Saturday to 23:00 on Saturday, and Saturday has 25 hours. Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Please show references to these clocks that indicate up to 25 hours at DST end and 23 hours at DST start. Cultural references to time adjustments like DST, leap seconds, and leap years, tell you very little about how clocks are expected to operate. The North American power industry refers to the 25th hour, which is the repeated third hour, as hour 2*, and military time usage runs from 0100Z to 2459Z to avoid midnight confusion, instead of 0000Z to 2359Z, but all use the same clocks. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised.
2018-09-08 22:13, Brian Inglis <Brian.Inglis@systematicsw.ab.ca> wrote:
On 2018-09-08 01:50, Phake Nick wrote:
2018-09-08 15:36 "Paul Eggert" wrote:
On 2018-09-08 01:17, Phake Nick wrote:
The law cited in the latest commit do say the DST en at 00:00 on the day after the second Saturday in September, however the second line of the law write that "the Second Saturday in September would have 25 hours in a day". Those mean the same thing. Since DST ends at 00:00 the day after Saturday, the clock jumps back from 24:00 on Saturday to 23:00 on Saturday, and Saturday has 25 hours. Not really. It would mean the Sunday's clock go to 24:59 before jumping to 00:00 on Sunday. The official time the DST end is "00:00am on the next day after the second Saturday of September". So it isn't ending before the day change.
Please show references to these clocks that indicate up to 25 hours at DST end and 23 hours at DST start. Cultural references to time adjustments like DST, leap seconds, and leap years, tell you very little about how clocks are expected to operate. The North American power industry refers to the 25th hour, which is the repeated third hour, as hour 2*, and military time usage runs from 0100Z to 2459Z to avoid midnight confusion, instead of 0000Z to 2359Z, but all use the same clocks.
-- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
This email may be disturbing to some readers as it contains too much technical detail. Reader discretion is advised.
I was made aware of the situation with the NICT interview that I posted in the first message, with NICT being the official authority to maintain and distribute the JST standard clock, and that in the article it's said that DST end at 25h back then. I see there are some newspaper back then which would have relevant information but I don't have any subscription that would allow me to access old newspaper database back then to check the words. Maybe we should just send a message to NICT and ask them about it to be sure?
participants (5)
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Alexander LIVINGSTON -
Brian Inglis -
Paul Eggert -
Paul G -
Phake Nick