From: "Clarissa Gammel" <cg@pc-plus.de> Date: Tue, 7 Apr 1998 09:59:44 PDT How often are there changes to the time difference information (approximately)? It averages about once a month. (But it's bursty.) How many countries are there with different time zones in one country? That depends on how you count. Do you mean different time zones now, or different time zones at some point in history, or a differing set of time zone histories? It also depends on what you consider to be a ``country''. Is Antarctica a country? That being said, here's a list of countries in the current TZ database that have multiple time zone histories. The first column uses the ISO 3166 country code, the second is the number of time zone histories. As you can see, Canada is the current champion, but this is to some extent an artifact of the tz database's cutoff date of 1970. The US would undoubtedly be the real champion in a complete database. $ awk '/^#/{next} {x[$1]++} END {for (i in x) if (x[i] != 1) printf "%s %2d\n", i, x[i];}' <zone.tab | sort +1nr +0 CA 21 US 20 RU 13 AU 10 BR 7 AQ 6 AR 6 CN 6 FM 4 MX 4 ES 3 GL 3 ID 3 KI 3 KZ 3 PF 3 PT 3 UM 3 CD 2 CL 2 EC 2 GB 2 IL 2 JP 2 MH 2 ML 2 MY 2 NZ 2 SJ 2 UA 2 Who provides that information? Volunteers. Their mailing list is <tz@elsie.nci.nih.gov>. Is it a governmental institution? NCI is a governmental institution, but it's merely a host for the mailing list. The real source of info is volunteers. The chief volunteer is at NCI. When in general are the dates for those changes? Are they regular, or each year different? Are there any rules? Not really. Which countries do or don't have summer or winter time? Generally speaking, the further you get from the equator, the more likely you'll have daylight saving time. But for the exact set of countries at any point of time, you'll need to consult the database at <ftp://elsie.nci.nih.gov/pub/>.