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    Re: Using the sun's direct and reflected image to determine a sextant's IE
    From: Tony Oz
    Date: 2020 Mar 9, 12:26 -0700

    Dear Ed,

    All those "on scale", "off scale" labels SHOULD be forgotten once for all - along with such remnants of the era of (algebraical) illiteracy as "same-name/contrary-name" mumbo-jumbo.

    Just use the algebraic sign!

    To obtain the value you should ALWAYS ADD (algebraically!) to the HS do:

    • measure the Sun's width by touching the direct and reflected images right-to-left (or upper-to-lower if you want) and then the left-to-right
    • imagine that the zero on the arc is marked as 360° and therefore if the index is to the left of it - read it as 360°mm', if the index is to the right - read it as 359°nn'
    • calculate 360° - (360°mm' + 359°nn') / 2

    This is the only way to do it properly.

    The bonus is that with the same 360°mm' and 359°nn' values you can check yourself:

    • calculate (360°mm' - 359°nn') / 4 and compare with the tabulated SDSun.

    It is 2020 today, not ~400 years ago, when people debatted wheater the "0" is a number like all others or if it is valid to operate with negative numbers...

    Warm regards,
    Tony
    60°N 30°E

       
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