On 2020-06-14 19:17, Paul Eggert wrote:
On 6/14/20 9:08 AM, Michael H Deckers wrote:
Is it really so hard to understand that this must have happened when UT was 1911-03-11T00:00:00, and not when UT was 1911-03-10T23:50:39 or 1911-03-10T23:55:39 (or even at different instants for the two time scales)?
This reminds me of the difference between the American way of doing DST transitions (all transitions are at 02:00 local time) versus the EU way (all transitions are at 01:00 UTC). The American way is easier to explain to non-experts, but causes sloppy execution (there are periods where New York is temporarily the same as Chicago, for example). The EU way is more logical and has simpler consequences (Paris is always exactly one hour ahead of London), but is harder to explain to non-experts.
Although the method you're suggesting for the 1911-03-11 French transition is more logical and has simpler consequences, that doesn't mean it corresponds to how civil-time clocks behaved or to how people thought they should behave. Perhaps they thought the transition meant "turn the clocks back at midnight" or "stop the clocks at midnight" (either of which is easier to specify to non-experts). At this point we don't really know.
Time changes are a spec for what has to happen to keep society organized. How that is implemented will vary depending on the potential impact on an organization. I don't think anyone on this list should pay any attention as to how particular organizations implemented changes: those are all merely implementation details, important to those organizations functions, but not anything that concerns anyone else, including this list, unless sufficiently outre to be mentioned. Systems and time/frequency organizations will note the offset change and keep on ticking. Some may stop some clocks and processes to avoid issues. Some electronic clocks may correct themselves, updating their display in some manner. Most will just change their time pieces, either centrally if they have such a system, or individually, at some point in time convenient to their staff, similar to everyone in their homes. Marine broadcast organizations would have sent out Notices to Mariners via maritime organizations, maritime news and weather broadcasters, and in messages during their own broadcasts. -- 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. [Data in IEC units and prefixes, physical quantities in SI.]