[tz] What is LMTZ?

Brian Inglis Brian.Inglis at systematicsw.ab.ca
Wed Sep 18 16:45:06 UTC 2013

On 2013-09-18 10:17, Lester Caine wrote:
> Alan Barrett wrote:
>>>> You often mention "LMTZ".  What does that term mean?
>>> It was my attempt at separating the early LMT times everywhere, and the early
>>> standardisations to an LMT based 'zone'
>> What is an LMT based zone?  Zones are geographical areas, whereas LMT is
>> associated with points.
>>> Naively I assumed that would be an easier transition than it obviously
>>> actually is? So we just move the switch-over point from 'location' based time
>>> to timezones?
>> Sorry, I am still too confused about your terminology to try answering that.
> Hopefully we can agree that pre standardisation, people based their local time
> on 'midday' which is what what Local Mean Time is. and different locations have
> a different offset. Anything on the same longitude will be the same time.
> When people started standardising they agreed on a Local Mean Time that applied
> across a bigger area. Now while towns may be on the same longitude their time
> offset would be different depending on the other locations in their group? I'm
> probably wrong but I am fairly sure that 'summer-time' or 'daylight saving is a
> 20th century invention? So prior to that all time was 'mean time' and it just
> depended on which longitude was being used to set it. 1915 started messing
> things up with the first varying time rules?
> Up until 1915 all we need to know is how the 'offset' from LMT was set when
> groups of locations agreed on a standard ... which is my 'LMTZ' data.

I think you may be saying that standard time really just follows LMT at some 
other location or longitude, and LMT for a location is set from that location's 
longitude; LMTZ documents pre-DST zones using an offset from some other 
arbitrary location's arbitrary longitude e.g. the local university observatory.

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