Hello Much of this is probably off topic, and may be wordy for many of the people on this list, but I have some questions about the historical meanings within the tz files, and how the files could be extended backwards for further date/time studies before 1980 & 1847. Perhaps my questions should be directed to calendar historians within this list, but here's what's on my mind.. - I am particularly interested in the meaning and accuracy of the opening entries for each tz zone. Almost every zone starts with an LMT record. For example, For Europe/London, the opening record states: Zone Europe/London -0:01:15 - LMT 1847 Dec 1 0:00s Does this mean that the city of London decreed that all clocks in the city of London should follow mean solar time with this pattern? Does this also mean that all, or most towns around London also synchronized to London time on the same date, or should I assume that on this date each city & town around London was expected to synchronize to their OWN local mean times? And what was the time-keeping standard before that date? I presume that many Brits where already using local mean times for their own towns before 1847, or should i assume that before 1847, most places in the UK where still using apparent solar times? For example: if I am researching Canterbury, on what date should I assume that it would start following its own LMT, and on what date would it start following London's LMT: before 1847, 1847, or later? Its easy enough to determine a location's apparent solar time, but determining when a place moved from apparent solar time to mean solar time, or then to a regional tz-based mean solar time is not clear to me. - Also - before 1847, I am curious about two other calendar-related issues... 1) For each tz zone, on what date did a preferred or decreed calendar change? (julian, gregorian, islamic, Chinese, French Republican, etc.). Most Catholic zones moved to Gregorian originally, but non-Catholic zones move to Gregorian on their own decreed dates. 2) For each zone, on what date did the start of year change? (Jan 1st vs March 1st, for example). The above issues are important to me for comparative historical studies, and genealogy. I intend to starting keeping track of the these pre-Fleming calendrical rules - yet using tz's zone names for synchronization - and making it freely available for others if it has not already been done. I'm willing to take it offline of this list and maintain it myself and for others for free download. Would there be other people on this list, or calendar historians, that would also be interested in me keeping this information in a usable standard format, and would people be interested in providing data, references and updates for a pre-tz calendrical preferences database like that I've mentioned above? Feel free to reply to me off this list, or on, whichever is most appropriate. I'm also willing to start a separate mailing list if its warranted. Thanks David Patte Relative Data, Inc.