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    Re: Sight reduction formulae
    From: Jaap vd Heide
    Date: 2011 Dec 2, 04:09 -0800

    Dear John,

    Your book has kept me busy and happy on the train, right next to the ex-meridian puzzle by Greg, thank you for that! :)
    But it would have been clearer to start the section on direct calculation with a statement it is based on a calculator with -very- limited capabilities. (it took me a while to realize you are replacing the value in Mem3 (STO3) halfway the calculation)
    My 15 years old then-not-so-cheap casio fx-4500p has 26 memory positions *and* allows me to enter angles straight in x°x'x" or x°x.x' in one go, so the stroke-by-stroke procedure differs quite a bit for me. :-o

    As for the OP's question:
    The sign in the formula is always "+" when signs are assigned to L and d values (+ for N, - for S).
    For the cosines in the first part of the formula nothing changes, for the sines in the latter part it does. (sine of a negative value renders a negative value) If both are negative (thus the same name), the latter part becomes the product of two negative values which renders a positive result. If one of the terms is negative, the product renders a negative result. Adding a negative number is like subtracting the absolute value of that number. But that doesn't change the sign in the formula.

    Kind regards,

    Jaap
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