[LEAPSECS] Consensus building?

Gerard Ashton ashtongj at comcast.net
Thu Feb 3 10:25:06 EST 2011

On 2/3/2011 9:00 AM, Clive D.W. Feather wrote:

> 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-".


The citation provided by Feather (provided you go to page 32 of the PDF,
which is page 124 of the brochure) proves the minute, hour, and day are
"Non-SI". Then of course there is relativity; the reference frame for
TAI is defined while the SI second may be measured in any reference
frame you wish.

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