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    Re: Reeds or W Hall
    From: Ducruy Jacques
    Date: 2015 Aug 4, 03:13 -0700

    Hi Paul,


    Thank you very much : your study is very clear.

    The only difference with the Reed's table : Hall give only Log Cos, Reed's give directly log cos and  log sin : so, you can calculate the azimut by sinus formula easily (but with lack of precision is Z is near to 90°).

    It is also interesting to study the evolution of versine formule :

    Douwes formula : Sin Alt = Sin Mredian Alt - (Cos D Cos L Vers HA)

    Lynn formula (1827) : Vers DZ = Vers (L-D) + (2 cos D Cos L Sin² HA/2) ... or : 2 sin² HA/2 = Vers HA

    Conclusion : the formula used by Hall is the same of the formula of Lynn !

    And we can adapt this formule with haversine :

    Hav DZ = Hav (L-D) + (Cos D Cos L Hav HA) => Davis formula ?

    Best Regards



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