[tz] What data should TZDB offer?

Clive D.W. Feather clive at davros.org
Mon Jun 7 19:14:00 UTC 2021

Paul Eggert via tz said:
> > In my own code I use 1800 as the transition date between LST and LMT 
> > when it's not specified elsewhere.
> 1800 is surely a bit early, for all but the most 
> technologically-advanced locations. In most of the world, solar time 
> maintained its supremacy over local mean time well after 1800.
> Part of the problem is that people in the early 19th century didn't much 
> care whether they were using local solar time or local mean time, and 
> many towns actually observed a mean-time approximation to solar time. 
> This state of affairs didn't change until the telegraph made it feasible 
> for timestamps to be communicated more accurately, and railroads needed 
> more-accurate time.

I was wandering round the Fitzwilliam Museum in Cambridge the other day and
noticed a Thomas Tompion (1639-1713) clock. It had two hands and a dial
with Roman numerals I to XII twice going round it. Outside that, in Arabic
numerals, were 5, 10, ..., 60, also twice. At the top it said "EQVAL 60 TIME".

Immediately outside that was a ring which could clearly rotate separately.
This also had 5, 10, ..., 60 on it twice, with "APPARET 60 TIME" (tilde
over the first E) at the near top - it was rotated so that the 60 was
aligned with 13.6 on the main dial.

(Clearly the staff don't know how to set it correctly, since the equation
of time was 3.22 that day.)

So 1800 is perhaps a bit late, at least for some places.

Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
Web: http://www.davros.org  |   - Henry Spencer
Mobile: +44 7973 377646

More information about the tz mailing list