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    Re: Ex-Meridian Sight using Inmans
    From: David C
    Date: 2020 Jun 13, 22:34 -0700

    Greg wropte

    David,  If you are using an artificial horizon and making observations with a metal sextant equipped with an optic then sub 1 minute of arc on an intercept should be the norm unless the wind is really blowing.

    Technique is important. I indicated that my sights were typically accurate to two or three moa. Today was another typical Wellington winter day with blue skies, no wind and a pleasant 12°C. After practice I manged to get the error down to <1'.  Instead of  taking the sight when the limbs appeared to just touch I took it when they seemed NOT to touch.

    Errors when limbs touched. Sights taken from 11 56 am to12 09 pm apparant time.

    -1.8  2.1   1.7   1.5  -2.3   -1.8  0.3  0.9   -0.4   -1.8

    Errors when limbs did NOT touch. Sights taken from  01 33 pm to 02 06 pm apparant time.

     0.0   0.4   0.4   -1.2   1.1   0.3   -1.6   -1.0   0.2

    There is another possible reason for my results. I have noticed that the lower the altitude the more accurate an AH sight is. I do not know the reason. Maybe  it is the greater rate of change of altitude with time when the apparant time is greater. The first set was taken at noon. The second set was taken in mid-afternoon. I made the last sight when it had become difficult to use the AH (lat 41S  dec 23N).

       
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