Pre-Fleming Calendrical Database

Paul Eggert eggert at CS.UCLA.EDU
Tue Mar 30 05:09:35 UTC 2010

David Patte <dpatte at> writes:

> Zone    Europe/London    -0:01:15 -    LMT    1847 Dec  1 0:00s
> Does this mean that the city of London decreed that all clocks in the
> city of London should follow mean solar time with this pattern?

No, it merely means that common practice in London was to use local time
before the stated date.  Whether this was actually mean solar time, or
some other approximation to mean solar time, isn't kept track of.  The
database currently approximates all the pre-standard-time stuff with
local mean time (a.k.a. mean solar time a.k.a. mean time a.k.a. mean
local time).  London is very much a special case, since here LMT stands
for "London Mean Time" as instituted by the Great Western Railway; this
is valid for Great Western stations in London but not for all parts of

> Does this also mean that all, or most towns around London also synchronized
> to London time on the same date, or should I assume that on this date
> each city & town around London was expected to synchronize to their
> OWN local mean times?

No, it's for London only.  It doesn't say anything about locations other
than London, for time stamps before 1970.  The only claim is that all
clocks in the Europe/London zone have agreed since 1970, and that the
entry is accurate (as far it goes) for time stamps in London itself
before 1970.

> And what was the time-keeping standard before that date? I presume
> that many Brits where already using local mean times for their own
> towns before 1847, or should i assume that before 1847, most places in
> the UK where still using apparent solar times?

That's out of scope for the tz database.  The actual situation was
pretty chaotic (see the London example above) and is typically
quite-poorly documented (London is one of the best-documented, and even
so we don't at all know when each part of London switched).

> - Also - before 1847, I am curious about two other calendar-related
> issues...

Calendar issues are out of scope as well; this is discussed in the
Theory file.

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