NavList:

Thanks for the replies. It is a very interesting subject.

I will download the Ageton-Classic pdf and give the method a try. I am on the look out for a copy of Dreisenstock  (and other tables). I can probably find a pdf online but I would prefer to work from a paper version if I can.

Yesterday I downloaded the 1864 Nautical Almanac and realised that it is probably impossible to replicate the work load of 19th century navigators. The navigator had to deal with Right Ascension and the Equation of Time. In addition the RA was tabulated once per day, unlike the Aeronautical Almanac  in which GHA  is listed at 10 minute intervals. Also the navigator had to calculate GMT from the rate of the chronometer - a trivial task today with a calculator.

Someone asked why the hav-cos formula replaced the sin/cos formula. My understanding is that it was to avoid having to take logs of negative numbers.

I have just checked the local weather forecast. The sun is likely to be out of commission for the next five days so I will have plenty of time to study the theory (-;