There are two issues that need to be distinguished: 1) leap years and leap seconds correct for precession/preserve seasonal alignments;
2) elapsed-time measurements [typically] deal in the difference D = t(j) - t(i), j >= i. For 2) consideration of leap seconds is not just otiose, it is wrong. For 1) it is necessary. Consider the case of a pair of microsecond-scale time measurements on either side of some midnight upon which a leap second is added to Gregorian time. Would you really wish to have a value of the form v = 1000000+a µsec figure in a sequence for which mean(v) was 10 µsec? More generally, think before you post. --jg On 1/12/12, Fred van der Windt <[email protected]> wrote: >>>No use of the TIME macro need or should figure in this operation. Any >>>leap-second corrections would, for example, be washed out by the >>>subtraction: >>> >>>(T + L) - (t + L) = T + L - t - L = T - t. >> >>Only if the interval t-->T does not span the introduction of the Leap >> Second. If t is in Year X and T is in Year X+1 then if the last minute >>of year X is 61 seconds long, your interval T-t will be off by one second. > > Not really: not in seconds anyway. If the interval contains 10 'normal' > seconds and the leapsecond the application will calculate a length of 11 > seconds which is correct. Things might get a little bit weird if we try to > convert the seconds back to minutes, hours and days that passed and > attribute those to the actual (calender) date and time. Suppose your > application starts running at 00:00:00 on a day with a leap seconds and ends > after exactly 86401 seconds. One might think that it ran for 24 hours, 0 > minutes and 1 second and thus 'spanned' two days. But in fact it ran for 23 > hours, 59 minutes and 60 seconds and ran *exactly* from start till end of > one calender day. > > It might not be a big thing for most applications but I'm sure there are > circumstances where this makes a difference. The cpu-cpin during the > leap-second probably prevents a lot of issues: it should prevent the > scenario I just mentioned because an application cannot run till the end of > the leap second: it would either end before the leap second or after the > leap second on the next day at which point it's run did span two calender > days. > > Fred! > ----------------------------------------------------------------- > ATTENTION: > The information in this electronic mail message is private and > confidential, and only intended for the addressee. Should you > receive this message by mistake, you are hereby notified that > any disclosure, reproduction, distribution or use of this > message is strictly prohibited. Please inform the sender by > reply transmission and delete the message without copying or > opening it. > > Messages and attachments are scanned for all viruses known. > If this message contains password-protected attachments, the > files have NOT been scanned for viruses by the ING mail domain. > Always scan attachments before opening them. > ----------------------------------------------------------------- > -- John Gilmore, Ashland, MA 01721 - USA
