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    Re: Precision clock
    From: Fred Hebard
    Date: 2008 Jan 10, 14:11 -0500

    The device to which you are referring, as far as a stopwatch is
    concerned, is called a lap counter.  Most new, inexpensive digital
    stopwatches have them.  You would still hack the watch off WWV or
    whatever, but when you stopped it to record the time, the main
    counter would keep on ticking, just the display would be frozen.  I
    suppose you could keep the watch going for several days or months to
    see whether it drifted much.
    One reason wristwatches might not drift much is that they are mostly
    held at a constant temperature by conduction from your body.  A free
    standing quartz stopwatch might drift more than a wrist watch.
    You should be able to get 1-second position accuracy or better with a
    theodolite.  As you note, a limiting factor is accurate timing.  A
    few years ago, Paul Hirose provided some links about the U.S. Coast &
    Geodetic Survey and telegraph timing back in the mid 1800s.  In them,
    reference is made to various procedures developed then to increase
    timing accuracy.
    Fred Hebard
    On Jan 8, 2008, at 5:10 AM, Geoffrey Kolbe wrote:
    > I am trying to use a theodolite with which I am trying to take
    > precision
    > sightings on stars, but a limiting factor is that virtually all quartz
    > clocks/watches only tick off the whole seconds, which immediately
    > limits me
    > to 0.25 minutes of longitude.
    > Is there a stopwatch out there that can be set to GMT so will act as a
    > chronometer over a period of weeks or months, but has a feature
    > where a
    > button can be pressed  and the display will show the time at which the
    > button was pressed to a tenth of a second or better? Then, at
    > another press
    > of a button, current time is displayed once again in the normal way.
    > Thanks.
    > Geoffrey Kolbe
    > >
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