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    Re: Position discepancy
    From: Gary LaPook
    Date: 2011 Dec 13, 14:04 -0800
    The Hc from the site is not what would have been measured with a sextant. If you are using a nav program that reduces a sight for you then it probably needs as an input the sextant altitude to which it will make corrections to come up a fix. So, you probably need to UN-correct the value you take from the almanac program and then use that value to put in the reduction program. For instance, you will need to add the refraction correction also found near the right of the almanac table to the Hc. You nav porgram should also take as inputs you height of eye (or dip) set to zero and set index error to zero. For Polaris and Jupiter that should solve your problem. Go back and compare your errors with the refraction corrections for the same time and place and body, they are probable the same.

    gl

    --- On Tue, 12/13/11, Fred Stevens <fredstevens@yahoo.com> wrote:

    From: Fred Stevens <fredstevens@yahoo.com>
    Subject: [NavList] Re: Position discepancy
    To: NavList@fer3.com
    Date: Tuesday, December 13, 2011, 1:24 PM

    I guess I wasn't too clear, although Derrick Youn picked up on it. I took no sights. I used a GPS to get my location, used that info and a date/time to get the almanac data for Jupiter and Polaris, the computed my position which should have resulted in the same spot I started with but it doesn't. And, yes, Derrick the error is between 1 and 4 nautical miles.

    So, how is one to know which "Earth model" is being used?

    Fred
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