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    Re: GPS as a time authority
    From: Lu Abel
    Date: 2009 Sep 15, 11:06 -0700

    douglas.denny@btopenworld.com wrote:
    > I was told that the only way of doing it with sufficient accuracy pre-GPS 
    was to physically take a portable caesium standard (actually not that easily 
    portable and weighing quite a lot) by aircraft to the facility required.  The 
    chap who's responsibility was to take it would book an extra seat on the 
    aircraft next to him for the time standard in the name of Mr. C.S Clock  or 
    something equally silly.
    Ah, yes, but then you have to compensate it for relativistic effects due 
    to the standard's motion.  I remember when "portable" atomic clocks 
    first became available (late 1950s or early 1960s) Hewlett Packard (now 
    Agilent) bought one of them a first-class ticket on a series of flights 
    that circled the globe and discovered that it was off from its brother 
    that stayed on the ground by exactly the amount predicted by the Theory 
    of Relativity.
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