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    Re: Upper limb correction for moon
    From: Gary LaPook
    Date: 2013 Sep 12, 01:16 -0700
    Addition also has the advantage in that you can do a whole column of additions but must subtract one at a time. I posted a form for correcting sextant observations that only uses addition here
    http://fer3.com/arc/m2.aspx/new-way-apply-sextant-corrections-LaPook-jan-2011-g15459
    it works because, instead of subtracting from Hs, you can add the same number to Hc and get the same intercept at the end.

    gl



    From: Bill Morris <engineer@clear.net.nz>
    To: garylapook@pacbell.net
    Sent: Sunday, September 1, 2013 10:35 PM
    Subject: [NavList] Re: Upper limb correction for moon


    Frank writes:
    "Manual subtraction is more difficult than addition, and it is considerably more prone to error." Too right!
    For the same reason it is on the whole better to have index error of a sextant off the arc so that the correction is additive ("If its off, put it on").
    Similarly, it is better that a mechanical chronometer have a slight losing rate rather than a gaining one so that the correction is again additive.
    Bill Morris
    Pukenui
    New Zealand
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