[tz] 1911 France change from Paris to GMT

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Mon Jun 15 13:43:13 UTC 2020

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
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
Some may stop some clocks and processes to avoid issues.
Some electronic clocks may correct themselves, updating their display in some
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

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