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    Re: Using sun compass for calibrating boat compass
    From: Greg Rudzinski
    Date: 2014 May 8, 12:58 -0700


    If an azimuth were taken at the same time as a prime vertical observation then the assumed longitude could be replaced by that of the reduced LOP. Meridian angle is then improved so that a more exact calculated azimuth can be determined by formula:

    Z = (Cos d) (Sin t) / (Cos Ho)

    Greg Rudzinski

    Re: Using sun compass for calibrating boat compass
    From: Bill B
    Date: 2014 May 08, 13:35 -0400
    On 5/8/2014 9:51 AM, Greg Rudzinski wrote:
    > The way I see this is that Hc is based on an assumed position not the
    > actual position so that the azimuths will differ slightly. Not an issue
    > for the LOP plot. But if an accurate fiber optic gyro were to be checked
    > to it's precision then I would use Ho (not Hc or Hs)to calculate azimuth
    > to the tenth of a degree.

    Sean and Greg

    Thanks for your input. I do see your points, but still feel like a puppy
    chasing its own tail.

    If I understand correctly, in the following formula I would still be
    working from an assumed position as the LHA is derived from the GHA and
    AP longitude, so your caveats are still valid:

    Tan Z = sin LHA / ((cos LHA sin lat) - (cos lat tan dec))
    If tan Z is negative, add 180 to Z
    If hour angle is less than 180, add another 180 to Z

    If the scenario was similar to Greg's post from the archives, and I was
    working from about a known position (Ho and Hc theoretically equal),
    then the azimuth derived from the Hc or Ho would yield the correct azimuth.

    Have I caught up to my tail yet :-)

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