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    Re: Chronometer Suggestions
    From: Alexandre Eremenko
    Date: 2009 Jan 5, 15:39 -0500

    
    Dear Irv,
    
    I am not a real expert on chronometers, but let me explain
    what I do know. A chronometer is not expected "to show time"
    in the same sense your wristwatch is expected. They always
    applied corrections to chronometer time, and did not attempt
    to adjust its "going" to zero.
    
    The main difference between a chronometer
    and an ordinary watch is that a chronometer is expected to
    have a very constant RATE.
    For example, it can be slow 1.5 seconds per day, and
    this is fine as long as this 1.5 remains constant.
    
    When chronometers were used for navigation, they applied
    daily correction to them. Once you check it in a harbor,
    and obtain an error, say T(0), the correction on the n-th
    day is
    determined by the formula T(n)=T(0)+Rn,
    where R is the daily rate. They did not try to adjust it
    to make R=0.
    
    Earlier (in 19-th and early 20-s century) they used more
    complicated formulas, taking into account the temperature
    of the chronometer which was measured by a termometer in
    the chronometer box.
    This was not done with the later chronometers because
    they are very well temperature compensated. This should apply
    to Hamiltons and Mersers as well.
    
    I never tried to adjust my chronometer,
    and it has daily rate of -1.88 sec per day
    (determined from
    two runs about 2 months each). When I use the above
    correction formula,
    it gives me the true time within a second on most of
    the days, say only 1-2 days in a month I obtain an error of
    more than 1 second, and never obtain more than 2.
    
    All this conforms to the factory specification.
    I did not test it at
    various controlled temperatures yet,
    as they do in the maitenance
    shops.
    
    I compare it with a good modern mechanical wristwatch
    (Swiss mvmnt ETA 2824-2). This watch looks BETTER
    for daily use:-)
    It deviates by less than 20 seconds in a month run. But it
    is not usable for navigation, without daily corrections.
    Because the rate is not constant: it goes one-two
    seconds ahead
    on one day and then one second behind on the next day, and
    this is UNPREDICTABLE. On one 15-day run, the average error
    was zero, but the maximal error
    on some days was up to 8 sec.
    
    And one more remark on your message:
    
    On Mon, 5 Jan 2009, Irv Haworth wrote:
    
    > I have two chronometers (both Thomas Mercer)
    > (Hamilton is more or
    > less the USA version)
    
    I doubt that Hamilton is a US version of Mercer.
    I read that Hamilton company delepoped their chronometer
    independently, starting from their railroad watch,
    and when I look at the movements
    they look completely different. I saw many claims that
    Hamilton 21 was the most accurate mechanical chronometer
    in the world in its time.
    
    Best regards,
    Alex.
    
    
    
    
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