[tz] Dealing with Pre-1970 Data

Steve Allen sla at ucolick.org
Sat Aug 31 16:24:06 UTC 2013

On Sat 2013-08-31T16:29:54 +0100, Lester Caine hath writ:
> Again, cart before horse, I'd been looking recently at time material
> based on sundial mid day and looking to incorporate that into my own
> time management stuff. I was getting around to the point of asking
> if anybody has a preferred estimation they use but decided this was
> not the right venue?

Even if this were the right venue, choosing a boundary for the
transition between local apparent time and local mean time is
just as arbitrary as a boundary for adoption of standard time.
As a result of the widespread use of chronometers the UK Admiralty
dictated that 1833 was the boundary for the Nautical Almanac, but
in the footnote added to the Future of UTC meeting 2 years ago
At Mystic Seaport library Frank Reed found logbooks with worked lunars
where navigators got aberrent longitudes because they had not adapted
to the change in the Almanac.  For non-navigational clocks of lesser
quality we should expect that resetting them according to some noon
mark was the practice until the local advent of telegraph and rail
modified civic practice.

Steve Allen                 <sla at ucolick.org>                WGS-84 (GPS)
UCO/Lick Observatory--ISB   Natural Sciences II, Room 165    Lat  +36.99855
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Santa Cruz, CA 95064        http://www.ucolick.org/~sla/     Hgt +250 m

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