[LEAPSECS] Caveat emptor!

[Joe Gwinn]

At 11:10 AM +0100 4/12/11, Ian Batten wrote:

>On 12 Apr 11, at 0903, Poul-Henning Kamp wrote:

>

>>  In message <7A41C92F-9BEC-4FDC-9809-071F2D624CF3 at batten.eu.org>, 

>>Ian Batten wri

>>  tes:

>>

>>>  and thereafter contracts would add "times in

>>>  this contract shall be assumed to be UTC" to the definitions section.

>>

>>  Don't forget that a lot of obscure contracts with large technical

>>  impact already states UTC explicitly:  Air Traffic Control, AIS

>>  Vessel tracking, telecoms accounting/settelment, NATO, meteology &c.

>

>It will be interesting to find out if there are contracts which cite 

>UTC by name and which also assume that UTC is a close-enough measure 

>of angular position, rather than TAI+constant.


In ATC, the desire is to ensure that everybody use the same time, and 
UTC is understood and distributed worldwide.

A good parallel is the altitude reported by transponders on aircraft. 
What is reported is the pressure altitude assuming an atmosphere 
without weather induced variations in atmospheric pressure.  The 
thinking is simple:  If everybody translated pressure into altitude 
the same way, vertical separation is ensured, as weather patterns 
vary quite slowly with distance compared to required separations.

Nowdays we correct reported pressure altitudes for local atmospheric 
pressure, to improve probability of correct correlation with radar 
data.

Joe Gwinn