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    Re: Chronometers
    From: Henry Halboth
    Date: 2008 Mar 29, 11:21 -0700

    Hi Alex,
    Although these references do not contain technical
    details on chronometer construction, you will find
    more information in the various editions of Dutton's
    Navigation texts. The later edition of 1985 broaches
    the subject of Quartz Chronometers ... "capable of
    maintaining an excellent rate, with the better models
    having a deviation of less than 0.01 seconds from
    their average daily rate that should not exceed 0.2
    seconds per day. Many models have a sweep second hand
    that can be advanced or retarded electronically in
    increments of 1/10 or 1/100 second while the
    chronometer is running." These instruments are battery
    operated, thus obviating the need for winding. This
    edition also broaches the use of atomic clocks for
    ultra-accurate navigational systems and missile
    guidance purposes, however, does not go into detail.
    I have used the commercial models of the so-called
    "atomic" clocks for sight purposes ashore and have
    found them to be satisfactory, but have no personal
    experience in their use at sea; I seem to recall
    having read that these commercially available time
    pieces are accurate to only withing 4-seconds,
    however, am unable to quote a reference.
    Older editions of Dutton, specifically that of 1934,
    which was my initial navigation text, details the
    older 20th century methods and procedures as followed
    by the US Navy. At that time well run ships, with
    presumably well heeled owners, carried at least two,
    if not three chronometers, and there was advocated a
    method of Chronometer comparison whereby the
    regularity of of daily rate could be demonstrated -
    using three chronometers it is possible to identify
    the chronometer whose rate has changed, while with two
    chronometers it is possible only to identify that the
    rate has changed. This comparison procedure of course
    presumes that a time signal is not regularly
    available; it is a boring procedure which at one time
    we had to learn.
    There are other texts that include commentary on the
    chronometer, Bowditch, Norie and Mixter being three
    that come immediately to mind, however, none that go
    into technical detail as to construction. To obtain
    any detailed specifics as to construction one would
    necessarily have to refer to watchmaking manuals, some
    of which deal in great detail with the chronometer and
    the methods of its manufacture.
    To increase the accuracy of reading the 1/2 second
    beat, I have sometimes used a 1/100 second reading
    mechanical stop watch running simultaneously with and
    synchronized with the chronometer second hand.
    --- Alexandre E Eremenko 
    > Henry,
    > Thank you for your interesting information.
    > > I suppose there might be some argument with
    > respect to
    > > methodology if the time between determination of
    > > errors was particularly great,
    > Strangely enough, I do not find any instructions on
    > determining the chronometer rate in the navigation
    > manuals that I have.
    > I would imagine the following procedure (before the
    > use of radio). While a ship is in a harbor, the
    > correction
    > would be determined daily by the time signals
    > (gun shots, falling ball). From this the daily rate
    > will
    > be derived. And then used until the next harbor with
    > time
    > signals.
    > > daily rate of 1.5 seconds losing. From a practical
    > Very close to my chronometer: my one is loosing 1.37
    > sec
    > per day so far, and this is constant within a
    > second.
    > Here is a difficulty by the way: how do I determine
    > the correction with say 1/2 second accuracy?
    > The chronolmeter clicks and shows every 1/2 second.
    > But my electronic watch (and Internet) clicks with
    > only 1 second frequency, so errors of comparison are
    > sometimes more than 1/2 second.
    > > point of view, it was customary to request a new
    > > chronometer be set slow so that the error be
    > additive
    > > -I guess true sailors didn't subtract too well.
    > That's a very good point!
    > Now I know why my chronometer is 1.2 sec slow:-)
    > By the way the factory certificate I have contains a
    > lot
    > of information from which I can infer how they were
    > tested.
    > I can post the details if there is interest.
    > I cannot repeat this test because it involvs
    > five 5-days periods
    > running under given constant temperature:-)
    > Alex.
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