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    Re: How Many Chronometers?
    From: Greg Rudzinski
    Date: 2009 Sep 15, 10:48 -0700

    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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