NavList:

Thanks all for comments on slide rules. Seems only celnav nav triangle (eg cosine )formulae for LOPs/Hc and lunars requires better than 4 places, most other things ok at 3 places, is that correct?(hence the use of cylindrical rules like the Bygrave and Fuller 2 for cel nav.). 

However, does anyone know the answer to my first question re the JS Letcher statement on page 92 that his version of the lunar clearance formula can be done satisfactorily on a standard trig slide rule, wheres he says on the same page that for lunars you have to use ultimate accuracy for exery step to 0.1'?

I shall now try it and the Karl formulae ( also page 92/93 in his book!) with my Thornton 1960s 10" (used it as a 15 year old for "o"  level and "A"  maths and physics!)and compare with calculator and Fuller 2. Happy days.

Best wishes

Francis