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

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Re: Longhand Sight Reduction
From: Hanno Ix
Date: 2014 Nov 23, 14:09 -0800
Greg,

Sorry , I missed that.

You know, personally, I don't use the "contrary" and "same" convention.
Years of math by hand trained me to watch out for signs when
adding and subtracting - got bitten too many times. The advantage is,
of course, one doesn't have to remember special sign rules.

My choice of letters was simple:
N: negative as in L-D, P: positive as in L+D; Q: well, next after P :)

Boy, what a compression of formulation, though - I am so happy about that!

H

On Sun, Nov 23, 2014 at 1:06 PM, Greg Rudzinski wrote:

Hanno,

The formula varient that you show is actually what I used to format the index card reduction. It works well to save space. For same name N=hav(L-D),  P=hav(L+D). For contrary name N=hav (L+D), P=hav (L-D). For calculator reductions  Hc= Arc Sin [1-2(x),   x=N+(1-Q)*havLHA.

I prefer to us different letters where n=(L+/-d),m=(L+/-d), P=(1- (n+m))*havLHA, ZD=Arc hav(n+P). This way when Bowditch is consulted there is better agreement.

Greg Rudzinski

From: Hanno Ix
Date: 2014 Nov 23, 10:10 -0800

Greg,

there is a form of the hav-Doniol some people might prefer.
Mathematically, there is no difference to the original formulation.
Here it is:

define:   N  =  hav( L - D );

define:   P  =   hav( L +D );

define:   Q  =  N + P;

hav(s2s)  =  N + ( 1 - Q )* hav(LHA);

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