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    Re: Radio Synchronized Clock
    From: Jared Sherman
    Date: 2002 Feb 28, 12:04 -0500

    Dov-
     This (correcting a quartz count) was implemented around 1980 in a totally 
    sealed diving watch which I think came out under the name "Pulsar" before the 
    new company of that name. It was a hermetically sealed watch, solar cells for 
    the 'face' and an LED display on the 'shoulder' of the face. Besides the time 
    set buttons it also offered a calibration/adjustment mode, since there was no 
    way to open the watch for internal adjustment.
     Since then watch accuracy has improved, typically better than +-15 seconds a 
    month which is well beyond what the mass market pays atttention to. I don't 
    see any market incentive for a manufacturer to do better, unless you buy the 
    Casio GPS watch which will put the accuracy of 16 atomic clocks on your 
    wrist--without your need to manually adjust it.
    
     I've been told the radio watches use a power conservation algorithm. They 
    only turn on the receiver circuit near midnight (when the WWV signal should 
    be propogating, etc. at its best) and try to correct themselves once every 24 
    hours. If they miss the correction, then they become more agressive about 
    turning on and seeking it. This may vary with manufacturers of course...but 
    in any case the watch would only need to see "sky" once daily, since the 
    typical quartz accuracy of +-15 sec/month means it will still be within 1/2 
    second of "right" for the rest of the day.
    
    
    

       
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