On 2022-07-28 05:02, Paul Eggert via tz proposed changes in files:
africa | 3 ++- asia | 19 ++++++++++++------- europe | 13 +++++++------ northamerica | 18 +++++++++++------- southamerica | 15 ++++++++++++++-
In tzdb, the difference local mean time LMT - UT only plays a role for the switch from LMT to a grid time zone time (and sometimes back to LMT, as in Amsterdam). So the relevant quantity is LMT - UT as estimated at the time of this switch. In the best documented cases, the switch is precisely specified by law (as for Dublin); and one can assume that the legal authorities have specified the switch to (at least) a precision that they thought to be relevant for the local time observatories and the most demanding applications at the time (such as navigation). In less well documented cases, we have an estimate of LMT - UT by local authorities (eg, from Milne 1899) at an epoch close to that of the switch; if these local authorities used subsecond precision then we may assume that such precision was considered relevant. But where we do not have such estimates, subsecond precision seems to be unwarranted as it would imply the wrong uncertainty for the size of the jump. As a case in point, the estimate used in tzdb for LMT - UT at Jakarta comes from 1876, but the switch to the grid time zone time UT + 07:20 only happened in 1932. Clearly, the old estimate of LMT - UT cannot be taken as evidence at subsecond precision for the jump made 56 years later. Regardless of whether subsecond precision is justified in each case, the following points in the proposed changes also need attention: • Unsurprisingly, no change is proposed for backzone -- but this is bound to produce new inconsistencies: backzone/America/Cayman uses Kingston Mean Time KMT and should therefore be made consistent with America/Jamaica. • backzone/America/Rosario has not been maintained since 2002-04-04 (eg, it has wrong offset for Córdoba Mean Time CMT, has no DST 2007..2009). It should be dropped from tzdb since it is unclear how it is supposed to differ from America/Argentina/Buenos_Aires; otherwise it must be properly maintained, including the new offset for CMT. • Similarly, backzone/America/Argentina/ComodRivadavia does not agree with America/Argentina/Catamarca since 1970 because the former has not been maintained since 2005-08-22, while Catamarca has since been changed. (Having the sources in the same file certainly would have helped!) So ComodRivadavia does not even satisfy the purported criterion for members of backzone. Remove or maintain properly. • Zone Asia/Jakarta needs an UNTIL AT column #STDOFF 7:07:12.5 23:47:12.5 Michael Deckers.