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Although Bowditch explains it somewhat differently, I believe you have it
right. Bowditch subtracts the raw back sight from 180-degrees, then
reverses the sign of the IC and Dip, which amounts to the same thing -
just be careful as to when you subtract from 180-degrees.

On Tue, 10 Aug 2004 07:50:17 -0300 Jim Thompson 
writes:
> Neither Dutton's nor Bowditch explain back sight reduction in
> sufficient
> detail for me to be confident about the process.  My understanding
> is this:
>
> 1. Raw altitude = back sight.
> 2. Corrected raw altitude: apply Index Correction and dip.
> 3. Corrected hs = 180d minus corrected raw altitude.
> 4. Then reduce the corrected hs as usual.
>
> True, or bungled?
>
> Jim Thompson
> jim2@jimthompson.net
> www.jimthompson.net
> Outgoing mail scanned by Norton Antivirus
> -----------------------------------------
>

   

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