NavList:

Frank,

Thanks for the fascinating insight into the  Thompson lunar tables. I've just found a free google PDF copy. Brilliant. (Gary, I would love to see more infromation on that 3ft slide rule!)

You said "Thomson's was a series method and therefore it could easily be worked up on some sort of slide rule. This is in marked contrast with the direct triangle, long form solutions of the lunars clearing problem. "  

I've always wondered how it is that JS Letcher claims adequate accuracy with  his series formula using a standard 10' slide rule only accurate to 3 places. 

Could you explain to this maths simpleton why this is so, but not for the direct triangle form which apparently needs 4+ place accuracy (as per my Fuller for example).

Thanks for all your help.

Francis