Keean Schupke k.schupke at imperial.ac.uk
Wed Jan 26 09:17:56 EST 2005

>Seriously, though, what use is being able to find the difference between two
>times like this? If I want the difference between two times, I want to
>specify in what units the difference should be e.g. millisecs, seconds,
>days, years, etc. The difference between times tA and tB might be 86400
>seconds, but they might still be on the same day e.g. leap seconds, so if I
>ask for (diffDays tA tB) I might get zero, one, or two, depending on the
Yes timing between point in time should be independant of leap seconds,
so if a program, takes 5 seconds to run it should always take 5 seconds, 
if it runs accross midnight.

This is why you want to be able to take the difference in abslute time. 
In which case if
you wanted an absolute number of days, you would take an average or 
standardised day length.
(Days are not really a satisfactory unit, perhaps kilo-seconds?)

You also might want to get a real difference, in which case you convert 
the start and end
times to localtime, and then take the difference.

Localtime is no use for measuring intervals as some days are longer than 
others... (so to know
exactly how long something took you would have to know how many 
leap-seconds fell within
the time interval)


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