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    Re: Longitude sight, South Pacific, 1864
    From: Frank Reed
    Date: 2018 May 13, 19:21 -0700

    Ed, you wrote:
    "pre-cleared Lunar ends up 117°49'16" after both semi-diameters. Can't account for the 1' subtraction, certainly not augmentation which would have been additive."

    Considering its position in the sequence of corrections, I presume that the 1' is nothing more than the instrument error or what we call today "index correction". In other early sights, this is simply labeled "Corr" for correction. I wonder when the modern term became common... 

    Frank Reed

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