On 2024-05-24 16:29, Steve Allen via tz wrote:
I urge great caution for the use of subsecond offsets.
Yes, and even offsets with one-second precision are dicey for older civil time; see, for example, the comments in 'europe' about Dunsink Mean Time. The subsecond offsets are put in mostly just to document the legal or announced definition of local time. Come to think of it, it's not entirely clear that Bern Mean Time legally corresponded to 7° 26' 22.50". The source for that meridian is here: https://www.admin.ch/opc/de/classified-compilation/20071096/index.html but this comes from government publications dated May 2008. It'd be better to cite a source for BMT during the period 1853 to 1894 when it was actually being observed. From the point of view of TZif files the subsecond offsets are all trivia, since the subsecond info doesn't affect them.