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    Re: Heath Sextant P356 - reading the vernier scale
    From: Alexandre Eremenko
    Date: 2018 Nov 28, 17:21 +0000

    The main scale is not well visible on your photo, but I suppose each degree is 
    divided into 6 parts on it.
    Which means 1 part=10'.
    First you look where the arrow on the vernier points. If it points exactly 
    against a division line, you have degrees
    and minutes; the number of minutes is divisible by 10. 
    Usually it will not point exactly. Then you take the closest line on the 
    right. This gives you degrees and tens of minutes.
    Then you scan the vernier left to right (looking through the magnifying glass) 
    and find the line on the vernier which matches
    some line on the main scale. You have to look carefully to determine this line 
    of best match. Then you determine
    which line on the vernier it is. The vernier is divided into 10 big parts each 
    indicating one minute. Then each such part on the vernier
    is divided into 6 part. So one part is 10''.
    So you read (up to 10) minutes and tens of seconds on the vernier.
    Add this to  the result which you read on the main scale.
    Remark. Various modern tables use tenths of minutes instead of seconds.
    To use these tables you convert the reading 10''=0.17' and then round to 0'.1.

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