Warner Losh said:
>> SI
>> - the SI-second is a standardised unit of measurement
>> - the SI-second is currently defined as a fixed number of transitions
>> of a caesium atom
>> - the current definition of the SI-second was ratified in 1967
> 
> Agreed.  I'd also add
> - the SI-second forms the basis for many other fundamental units of measure.
> 
>> - an SI-based-minute is formed from exactly 60 SI-seconds
>> - an SI-based-hour is formed from exactly 60 SI-based-minutes and thus
>> exactly 3600 SI-seconds
>> - an SI-based-day is formed from exactly 24 SI-based-hours and thus
>> exactly 86400 SI-seconds
>> 
> These are true only most of the time.  On leap second day, they are all 
> false and off by 1, typically one low.  It all depends on the timescale 
> that you use, and thus there can't be a universal definition here.

Actually, Stephen is right and you're wrong. The BIPM defines an SI minute,
hour, and day in exactly this form. See table 6, page 32, of:
http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf

This, of course, implies that "SI-based-" is the same as "TAI-".

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