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Thanks Jaap,

yes I now understand the Cosine method from Erik de Man's site. i shall try A3 graph paper + accurate drawing board and vernias to try to increase accuracy. Early experimetns with an enlarged Brown-Nassau graphical slide rule + magnifier+ vernia suggests a possible accuracy to 1-2' ( under the best indoors conditions, not thrown around in a seaway!). Yes, John karl's book says it all really in terms of theory.

On equestion you may help with, but only if you find it interesting, i have done lunar clearance with th BN using John Karls page 89.

essentially we use dec =hsd, lat=Hsd,Hc = LDsd and we want to find diff in AZ (RBA) so that is same as unknown LHA.

Are you able to figure out how to use the Eric de Man cosine method to do that? I think it should be possible  if it works wth the BN, I think the formula would be cos RBA=(cosHC-sinlatxsin dec)/coslatxcosdec .

Don't worry if you do not have time or not interested.

thanks for directing me to de Man method. Great fun!

Francis