On Mon, 5 Aug 2024 at 12:09, Eitan Adler via tz <tz@iana.org> wrote:

I'm interested in some specific timezone history. Specifically I'm
curious about the origin of 'STDOFF 0:19:32.13'. Does anyone have an
authoritative source for where this is derived from?

For one example, the backzone entry for Europe/Amsterdam contains the following comment:

# The data entries before 1945 are taken from

# https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm

Section III of that webpage (in Dutch) has a subsection entitled "Eenheid van tijd in Nederland" ("Unit of time in the Netherlands") which states that, though the law did not specify the Amsterdam meridian, there was a general understanding to use "the meridian of the Westertoren (4° 53' 01.95" east longitude), corresponding to a time difference of 19 minutes 32.13 seconds with UT. However, for the sake of convenience, a rounded value of exactly 20 minutes was usually used."

That page is the responsibility of Robert Harry van Gent and is hosted by the Faculty of Science at Universiteit Utrecht.

--
Tim Parenti