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Don't give up on this idea Hanno, you can always get satisfactory Az/Zn from Weir diagrams which I have rolled up inside my Fuller!. Easier amd quicker than  any slide rule. Just let me have a good explanation of the design re cursers and required sets/operations to do the Cosine formular,  and I will try it out in the next few days. Got major surgery  on 20th , so time is the essence! I think you may be on to something here.

Recently been looking at other methods, eg the Poor LOP, which used the haversine formula (my favourite log based method, again, because i get it)) and needed about 4 different scales (easy on a circular slide rule, but the Bygrave is the easiest.

Also, see Gary LaPook correspondance re the apparent innate superiotity of the Bygrave formula re accuracy versuus the cosine formula. Not sure  I understood it, but you may.

I have also now at last cracked how to do the full lunar clearance with just the Bygrave without any help from the mathematicians on site. more later when I have it confimed with some  more shots. I like the Fuller but really love the Bygrave.It now does my LOPs and my lunars.

Francis