[LEAPSECS] the abbreviation UTC

[Gerard Ashton]

On 8/18/2011 4:30 AM, mike cook wrote:

     Could this be a good argument for getting parking ticket offences 
thrown out?

Under current rules, UTC is an approximation to mean solar time at some 
meridian that passes through the grounds of the Royal Observatory, 
Greenwich (although not necessarily the crosshair of the Airy Transit 
Circle). The wristwatch of the traffic enforcement officer is an 
approximation to the mean solar time that is in force as civil time in 
the UK. Ignoring differences of one hour due to summer time, the 
difference between UTC and the civil time is probably less than one 
second. (It is less than 0.9 s between UT1 and UTC, and I would guess 
the various variations in the plausible locations of the meridian and 
the various algorithms for computing mean time would be less than 0.1 
s.) As a rule of thumb, higher accuracy standard should have a tolerance 
of 1/3 of a lower accuracy standard that is to be calibrated. Thus, if 
there is an uncertainty of +/- 1 s in the meaning of GMT, the traffic 
enforcement officer's wristwatch may still be calibrated with UTC 
provided the wristwatch need not have an accuracy of better than +/- 3s.

I would be most surprised if there is an actual written procedure that 
traffic officers must follow in setting their wristwatches and a 
specified grace period officers must allow before issuing a citation, 
but maybe the officers in the UK are better organized than the ones I've 
encountered in the USA.

Gerry Ashton