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Gary,

Thanks so much for your detailed and learned repy.Yes, this would be the best way of checking the Bygrave. So when not lazy and in a hurry (most of the time as old age creeps (= rushes) by, as Capt Aubrey said,"not a moment to loose!), I'll do this.For speed and checking BN, probably UNSO calculator or Andres app. (Also just looked at AP 29 for the first time in years and there they are!)

Out of interest, early tests suggest the BN is accurate to 1-2' if I stick to whole number Lat and LHA, avoiding interpolation errors or "guestimating" the  place of pencil dots between 1° curve lines,see previous posts on this) (Dec ok as is,because of the Vernia). Of course, one advantage of Bygrave is you can use ° and ' ok, but I get an early impression of slightly more consistent accuracy (1') if using whole number lat and LHA? Watch this space for morte test results.)

Again, many thanks as always

Francis