NavList:

Iv'e now done approximately 20 trial calculations with the full sized, polycarbonate model.

I get a mean accuracy Hc about 2-5', and generally in under 1 minute time. Az takes less than a minute to about 10-30' accuracy. Easier and quicker than Bygrave, but not quite as accurate. If you use whole interger degrees for LAH and Latitude, more accurate and just have to circle the appropriate printed dot on the base plate. the Declination accuracy is increased with the Vernia scales.

This definitve version, using brass post screws as pivot bearing ,requires very accurate drilling of bearing hole. (took me over 2 days or frustrating trial and error.) the simple, "drawing pin" bearing prototype using plywood base plate and laminated plastic transpareency sheets for the quadrants only takes about 2 hours to make and works fine.

So I hope Gary and Greg may test drive one of those on  a "Chichester Style" flight, compared to Bygrave? Build details of both models available  on request.

Best wishes

Francis