(If this is now where I should be asking these questions, I apologize -- please direct me to the correct source.) I am new at time zone information, so please bear with me. I have to develop a "Y2K Rollover Model." Looking for time zone information, I found the tzdata199e.tar.gz archive (at ftp://elsie.nci.nih.gov/pub/) -- which is great -- exactly what I needed. I believe that I understand most of it, but I have a few questions. Most of them are about the fine points of how the rules work: 1) From 'africa', Sierra Leone has the following entry:
# Sierra Leone # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S # Whitman gives Mar 31 - Aug 31 for 1931 on; go with Shanks. Rule SL 1935 1942 - Jun 1 0:00 0:40 SLST Rule SL 1935 1942 - Oct 1 0:00 0 WAT Rule SL 1957 1962 - Jun 1 0:00 1:00 SLST Rule SL 1957 1962 - Sep 1 0:00 0 GMT # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Africa/Freetown -0:53:00 - LMT 1882 -0:53:00 - FMT 1913 Jun # Freetown Mean Time -1:00 SL %s 1957 0:00 SL %s
1a) It is my interpretation that no rules apply after Sep 1, 1962 -- is this a correct interpretation? If not, please explain. 1b) If no rules apply, then what letters are used for SL time? (As I interpret it, %s would be blank if no rules apply. If this is not the case, please explain.) 1c) If no rules apply, why not specify a "no rules" entry, such as the following? (I would think it would be much easier [less ambiguous] for HUMANS to read, and thus less likely to contain mistakes.)
# Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Africa/Freetown -0:53:00 - LMT 1882 -0:53:00 - FMT 1913 Jun # Freetown Mean Time -1:00 SL %s 1957 0:00 SL %s 1962 Sep 1 0:00 - GMT
2) Please explain a "Numeric RULE", such as in the following example for Cape Verde:
# Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Atlantic/Cape_Verde -1:34:04 - LMT 1907 # Praia -2:00 - CVT 1942 Sep -2:00 1:00 CVST 1945 Oct 15 # <<< Please explain -2:00 - CVT 1975 Nov 25 2:00 -1:00 - CVT
3) Please explain "TYPE", such as in the following rule for South Australia:
# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule AS 1990 1994 even Mar Sun>=18 2:00s 0 - Rule AS 1990 1994 odd Mar Sun>=1 2:00s 0 -
4) For the rules shown in "4" above, what does the "s" on the "AT time" mean? I have also seen other letters, such as "u" -- what letters are used and what is their meaning? 5) Where is the format for the Zone, Rules, Links, etc. defined and the syntax for each entry documented? (If I could have found that info, I probably would not have had to bother you with all these dumb questions!) I GREATLY thank you for your time in answering all these newbie questions! Sincerely, Jon R. Kibler Systems Architect Year 2000 Services Manager Jon.Kibler@aset.com Advanced Systems Engineering Technology 389 Johnnie Dodds Blvd., Suite 205 Mt. Pleasant, SC 29464-2950 (Charleston) Phone: (843) 849-8214 Fax: (843) 849-8215