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    Re: An old Russian sextant certificate
    From: Lars Bergman
    Date: 2023 May 28, 05:26 -0700

    Frank wrote "Something I couldn't figure out: at the bottom of the calibration column, it says "R=22°  2E=69°". Any thoughts? Maybe a standardized eccentricity model??".

    Yes, it seems to be an eccentricity correction, where 2·R is the graduation on the arc closest to the arm's axis. 2E is actually 69'', where E is eccentricity/radius. Then the correction to be applied to a read value A is 2·E·(sin R - sin(R - A/2)).

    The parameters R and E are determined from two angle measurements that are compared with their true values, then the table for every ten degree is computed. The value for 70° is faulty.

    Assuming an 8 inch radius sextant, E = 69''/2 = 1.7·10-4 radians gives an eccentricity of 0.03 mm.


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