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    Re: Chronometers
    From: Paul Hirose
    Date: 2008 Mar 31, 11:52 -0700

    Alexandre E Eremenko wrote:
    > I understand the method of comparison of chronometers.
    > (It is described in many books, including Chauvenet).
    > My difficulty is in comparison of ONE chronometer with
    > internet or electronic watch, to high accuracy.
    If you can hear the chronometer ticks while observing the electronic
    watch, try the "eye and ear" method. Before chronographs, that's how
    astronomers timed the transit of a star to measure its right ascension.
    Chauvenet explains the procedure:
    In your case, the display of the electronic clock is the "star".
    engineer wrote:
    > When rating my two regulator clocks I work the other way around,
    > starting my stop watch on the minute by WWV on 10 or 15 MHz and
    > stopping it when the clock beats the minute. The difference is the
    > error. Hence it is easy to obtain a rate, no doubt dependent on
    > variations in my reaction time.
    I've found it easier to start the watch on some convenient tick (say,
    the tenth one) after the top of the minute, because you can pick up the
    rhythm and hack the watch on the tick instead of reacting to it. When
    doing this at the top of the minute, the missing 59th tick makes it
    harder since you have to carry the rhythm across a 2-second gap.
    After starting the watch, you can take splits on several WWV ticks to
    verify the stopwatch fractional seconds are close to zero. It's easy to
    hit the mark within a few hundredths of second.
    The stopwatch can also be hacked from a visual display instead of WWV.
    In fact, I'd rather use a stopwatch instead of the eye and ear method.
    It eliminates the need to interpolate fractional seconds by ear. I don't
    think I could do that better than the nearest quarter beat.
    During the eye and ear era, astronomers discovered that transit timings
    were often affected by a significant "personal equation". The difference
    between experienced observers could be surprisingly large. Bessel and
    Struve differed by a full second, according to Chauvenet.
    Didn't Maskelyne once fire an assistant because his transit timings were
    consistently off?
    Improvements in technology reduced the personal equation. Chauvenet
    mentions the chronograph for recording when the observer pressed a
    switch. The latter was replaced by a wheel with electric contacts on the
    shaft of the eyepiece micrometer. All the observer had to do was turn a
    knob to keep a wire on the star. Still later, an electric motor drove
    the micrometer, the observer simply making small adjustments to its rate.
    If Alex has a video camera, perhaps he can eliminate personal equation
    by simultaneously recording both clocks. Then view the recording one
    frame at a time to analyze the clock offsets.
    I block messages that contain attachments or HTML.
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