[LEAPSECS] draft revision of ITU-R TF.460-6

[Warner Losh]

TAI is a paper clock.  Measurements are made on real clocks, and a "retrospective" timescale is constructed from that data that gives the TAI time scale.  In effect, it computes the time difference for each clock so you can correct any measurements you made to TAI.

UTC, on the other hand, is actively measured and computed in real-time and physical devices are steered to be on-time and on-frequency for UTC.  This time scale is also broadcast in real-time, so you can steer your local reference clocks to be on time and on frequency.

In theory, this should allow TAI to be known to a higher degree of accuracy and precision since you are basically averaging more things together over a longer time period to get this clock.  There is data published that gives the delta between TAI and UTC(k) for various national labs's realization of UTC, but weeks or months after the fact.

Warner

On Dec 8, 2011, at 12:43 PM, Zefram wrote:


> Steve Allen wrote:

>> http://www.ucolick.org/~sla/leapsecs/draftTF460-7.html

> 

> "TAI is not physically realized and consequently is not suitable for

> time dissemination." -- what on Earth is that supposed to mean?

> 

> -zefram

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