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Looking again at my previous message, I seem to have messed up the logic of the last couple of sentences.  What I should have said is.  If you have to go into the almanac to get GHA Aries, you might as well get SHA star and declination at the same time and use simple arithmetic to calculate LHA star.  It’s difficult to see which bits move with respect to one another, but it would appear that if you set it up to get LHA star at a particular Greenwich Time, you can move the top disc to record its value as time progresses.  You must be able to do a similar thing with longitude to either calculate LHA from GHA or allow for the change of LHA with longitude, but to me it seems to make LHA increase with longitude west, which is wrong.  It should decrease.  Hence there is a need to see what’s written on the back. DaveP