Thanks Zefram and Paul for your ongoing assistance. I managed to find versions of zic.exe and zdump.exe that run in my Windoze environment (using GygWin64), and have played with them a little to see what they do (the documentation is a bit sparse). Zic produces binary data that looks like it will be of little use to me (since I don't know what it is!), but zdump produces a potentially useful ASCII output. Given that there's no simple way of finding the source file for a given region/city, I guess the logical thing to do is concatenate all the source files into one, and search that for the desired region/city. So I delved into Makefile and extracted the line that specifies the source files (PRIMARY_YDATA= africa antarctica asia australasia europe northamerica southamerica) and concatenated those files. I presume this set of files is unlikely to change in the foreseeable future? But zdump produces DST output in 'absolute date' form rather than the 'current rules' I'm looking for. The Arduino code (by Jack Christensen) I'm planning to use (since it's so well-written and does all the timekeeping and DST computation I need) runs on 'rules' (as indicated in my first post on 14-Oct-2017), not absolute dates, so I still need something that extracts current rules from TZdb, not absolute change date/times. But I think I can now extract those rules from the concatenated source files, using a parsing method much as I described in my 31-Oct-2017 post, modified as per Zefram's comments on 1-Nov (maybe 31-Oct in his timezone). And as Zefram said, most of this pre-processing can be done on my server. So a clock would simply send a query to my server (here's an equivalent human interaction!): "Have my rules changed in the last week?", and the server would reply either: "No, keep using your current rules" or "Yes, here are your new rules." Another issue to be decided is how my server checks your server, perhaps weekly, for updates. Paul mentioned 'get the Last-Modified: header', but I'm not sure what that is and how my server would get it. Ideally there's a way for a server to find out whether the TZdb has been updated without having to download files first. Regards, Daniel