How do you regulate a Hamilton model 21

Discussion in 'Chronometers' started by River rat, Dec 10, 2019.

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  1. River rat

    River rat Registered User
    NAWCC Member

    Apr 4, 2009
    I notice that on the Hamilton model 21 there's no regulator to regulate the time. Would it be the weights on the balance wheel that regulate it ? Being a novice I would not try. Am I right just never seen that talked about here yet.
  2. Tom McIntyre

    Tom McIntyre Technical Admin
    Staff Member NAWCC Star Fellow NAWCC Ruby Member Sponsor

    Aug 24, 2000
    retired SW dev
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    MvtMarks.jpg The model 21 is free sprung as are almost all marine chronometers. The reason is that the curb pins on the regulator degrade the isochronism slightly. When the hairspring is touching a curb pin it is shorter than when it is free from them and the amount of that interference depends on the amplitude of the balance arc.

    Free sprung balances have mean time screws or weights that are adjusted to achieve a useful mean time. It is not really necessary that the chronometer display correct time. It is only necessary that it maintains a steady rate. If the rate is known the apparent time can be corrected when calculating position by adding or subtracting the rate difference accumulated over the period since the machine was last adjusted.

    In the working lifetime of the Model 21, the rate could be determined more conveniently by the radioman providing the correct time from time broadcasts. The chronometer log book would have the discrepancy recorded whenever a valid time signal was received.

    The mechanism for adjusting the rate on the Hamilton is the two large nuts on the ends to the Invar arm with fine adjustments with the two adjacent vernier screws.

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