Nelson's Weblog: tech / good / zoneinfo

Time zone database

zoneinfo, the Unix time zone database, is good software. It converts absolute time to local time subject to local conventions, historical circumstance, and stupid laws. It has to work from at least 1970, so time-loving geeks have filled it with minute local detail about the inconstancy of local timekeeping.

# Part of Kentucky left its clocks alone in 1974.
# This also includes Clark, Floyd, and
# Harrison counties in Indiana.
Zone America/Kentucky/Louisville
  -5:43:02 - LMT 1883 Nov 18 12:16:58
  ...
  -5:00 US E%sT 1974 Jan 6 2:00
  -6:00 1:00 CDT 1974 Oct 27 2:00

The 2006b update contains the news that Indiana has now standardized their adoption of DST. It also has the fact that this year, Melbourne is delaying the adoption of DST one week to accomodate the Commonwealth Games. But that's all practical stuff; what's fun about zoneinfo is all the learned and detailed comments about local time jurisdictions. Paul Eggert is particularly eloquent.

Shanks writes that Michigan started using standard time on 1885-09-18, but Howse writes (pp 124-125, referring to Popular Astronomy, 1901-01) that Detroit kept

local time until 1900 when the City Council decreed that clocks should be put back twenty-eight minutes to Central Standard Time. Half the city obeyed, half refused. After considerable debate, the decision was rescinded and the city reverted to Sun time. A derisive offer to erect a sundial in front of the city hall was referred to the Committee on Sewers. Then, in 1905, Central time was adopted by city vote.

This story is too entertaining to be false, so go with Howse over Shanks.

tech • good
2006-04-01 18:03 Z


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