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    Re: Slide Rule Azimuth
    From: Gary LaPook
    Date: 2009 May 30, 05:12 -0700

    That is the formula that I have used for years for calculating azimuth.
    You can find it in Bowditch. George has pointed out that it gets
    ambiguous near east and west but it is not a problem in real life and is
    quick and easy to do on a calculator or slide rule. For those rare cases
    near east or west another formula could be use. The Az calculated with
    this formula is between zero and ninety degrees so you have to figure
    what quadrant you are in and convert to Zn but this is also not a
    problem in real life since you know the approximate direction when you
    pointed your sextant.   See:
    Greg Rudzinski wrote:
    > An interesting azimuth formula presented by H.H. Shufeldt in his book
    > Azimuth = INV SIN of  COS declination Sin meridian angle  divided by
    > COS altitude ( Ho or Hc )
    > Shufeldt states that Ho or Hc altitudes can be used. The INV SIN
    > result  is added or subtracted from 360 or 180 degrees depending on
    > orientation.
    > An alternate arrangement for the formula:
    > Azimuth = INV SIN of  SEC altitude COS declination SIN meridian angle
    > I like the expediency of this formula but it does suffer from
    > inadequate  slide rule scale resolution for azimuths approaching 270
    > or 90 degrees. A trick to by-pass this problem for a sun observation
    > would be to directly observe a corrected bearing of the sun (which
    > should be low in the sky) for use as an altitude intercept azimuth.
    > >
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