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    Re: How Many Chronometers?
    From: Werner Luehmann
    Date: 2009 Sep 15, 20:31 +0200

    Greg,
    Probably better than having the watch "in the wild". But how do you exactly 
    know the rate? It certainly still will depend on some (mostly uncontrolled)  
    variables, like the way the watch is worn (under sleeve or not), exposure to 
    sun  or aother infrared radiation. What a navigator needs is some certainty 
    on possible errors and not values by chance.
    Not be be misunderstood. Even a cheap quartz watch is far more accurate over 
    time than a many times more expensive mechanical one. It is well suited to 
    pick the time from an exact source (WWW etc) and use it for hours or even 
    days. That is how I use my stopwatches.
    The only cheap, reliable solution is a radio controlled watch. They are around 
    for less than 20 EUROS here in Germany.
    Although, for the fun of it,  I have a more expensive one (made by "Junghans") 
    that has a multi-frequency receiver working in central Europe, USA and Japan 
    (checked it). But on open sea ...?
    
    Werner
    
    Am Dienstag, 15. September 2009 19:48:52 schrieb Greg Rudzinski:
    > Werner,
    >
    > If an uncompensated digital watch is worn on the wrist(24/7/365) then
    > wouldn't this maintain the quartz at a consistent temperature?
    >
    > Greg
    >
    > On Sep 15, 10:21�am, Werner Luehmann 
    >
    > wrote:
    > > Sorry Gary, �wrong conclusion. The problem with quartz watches (or any
    > > quartz driven oscillator) �is their temperature dependance. Only under �a
    > > constant temperature you would get constant "rates". �For example, in
    > > high class radios the quartz is kept at a constant temperature higher
    > > than the ambient temperature in order to ensure frequency stabilty. In
    > > wrist watches compensating electronic devices can be used. But this is
    > > expensive and not found in 17 Dollars pieces, if at all.
    > > So unfortunately �this cheap solution doesn't work for us.
    > > B.T.W.: I have some nice digital (and not too cheap) stopwatches (made by
    > > the German manufacturer "Hanhart") that elected to adjust their rates
    > > according to the year's season ;-)
    > >
    > > Werner
    > >
    > > �Am Dienstag, 15. September 2009 11:22:33 schrieb Gary LaPook:
    > > > Based on our discussion, I became curious about the accuracy of digital
    > > > watches and their suitability for use as chronometers so I went to my
    > > > local TARGET store and purchased three identical watches for $17.00
    > > > each, the cheapest that they had. I set them and let them run for a few
    > > > days and, as I expected, they each had different rates. Based on this I
    > > > labeled them "A", "B", and "C" in the order of their rates starting
    > > > with the slowest. I then reset them to UTC at 0121 Z on May 28, 2009. I
    > > > checked them against UTC from WWV eleven days later on June 8th and
    > > > found that they were all running fast by 2, 4 and 7 seconds
    > > > respectively and I worked out their daily rates as .1818, .3636, and
    > > > .6363 seconds per day, respectively.
    > > >
    > > > On July 11th, 44 days after starting the test, the watches were fast by
    > > > 9, 17 and 28 seconds. Using the rates determined in the first 11 days
    > > > the predicted errors would have been 8, 16 and 28 amounting to errors
    > > > in prediction of 1, 1, and 0 seconds. If using these three watches for
    > > > a chronometer we could average the three errors and end up with only a
    > > > .66 second error in the UTC determined by applying the daily rates to
    > > > the three displayed times after 33 days from the last check against WWV
    > > > which took place on June 8th.
    > > >
    > > > I determined new rates now based on the longer 44 day period of .2045,
    > > > .3864 and .6363 seconds per day, respectively.
    > > >
    > > > On September 15th at 0800 Z (per WWV), 110 days after starting the
    > > > test, �I took a photo of the watches which I have attached. The photo
    > > > shows the watches fast by 21, 41 and 69 seconds but by carefully
    > > > comparing them individually with the ticks from WWV the estimated
    > > > actual errors are 21.5, 41.8 and 69.0 seconds. Using the 44 day rates,
    > > > the predicted errors are 22.5, 42.5, and 70 seconds giving the errors
    > > > in the predictions of 1.0, 0.7 and 1.0 seconds which, if averaged,
    > > > would have caused a 0.9 second error in the computed UTC after 66 days
    > > > from the last check against WWV on July 11th.
    > > >
    > > > If, instead, I used the 11 day rates then the predicted errors would
    > > > have been 20.0, 40.0, and 70.0 seconds which would result in errors of
    > > > prediction of -1.5, -1.8, and 1.0 which, if averaged, would cause and
    > > > error in the computed UTC of -0.6 seconds after 99 days from the last
    > > > check against WWV which would have been on June 8th in this example.
    > > >
    > > > �From this experiment it appears that fifty one dollars worth of cheap
    > > > watches would give you a perfectly adequate chronometer.
    > > >
    > > > gl
    >
    > 
    
    
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