# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Just getting started
From: Bill B
Date: 2007 Jan 19, 19:39 -0500

```> There is a section in the 229 for adjusting long intercepts to cause the
> LOP
> to better approximate a COP.  See Introduction > C > Special Techniques
>> 1.
>
> Bill
>
Doug replied
>
> It is much wiser, for consistency of method at first, to choose an
> assumed longitude for any reduction to be nearest to the estimated
> longitude so that the LHA will equal GHA minus west and plus east
> longitude in whole degrees. 30 minutes maximum of arc is a norm.

Let me first agree with you, and second restate.

There is a section in the 229 for long distances on the LOP away from the
the intercept to cause the LOP to better approximate a COP.

In the example in 229 they are adjusting a point along the LOP 45 miles from
the intercept. The intercept is approx. 16 miles long. That's a pretty big
miss using calculator methods, but I could see it happening in 229. Or in
traditional non-tabular reductions if the skipper had not been able to get a
fix for days, especially in a storm.

What to do?  List wisdom appears suggest if the DR/EP was that far off,
first recheck my calculations.  Then one might use an AP closer to where it
appears the craft is now to reduce the intercept length if possible, and the
distance along the LOP from the intersect.

My point is that in tabular methods, the above may not always be possible.
It is possible in the worst-case to have the AP longitude and LHA just shy
of 30' away from the the DR/EP position even if DR/EP was spot on.  This
could result in the AP being 42.x miles away from DR/EP.

My comment was only meant to make Gary aware that adjustments are possible
with 229.

Bill

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