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Author
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Topic: My mistake - misreading a 9 as a 4!
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Lance
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posted January 03, 2026 03:18 AM
I recently bought a new calculator and decided to test it by reproducing one of the sight reductions in the Starpath book "Celestial Navigation - A Complete Home Study Course". This is still my favourite text on the subject despite buying numerous others and I've yet to find a calculation form better than Form 104, although I've made one or two alterations to it for my own ease of use.
On page 96 there is a sample sight reduction for Venus. I decided to use that sample calculation to test my calculator procedure. I got it wrong. After a day I found my error. The problem was that I read the LHA as 42° - it's intended to be 92°.
In trying to find my error (and because I had a bout of insomnia) I calculated out every other sample sight reduction shown on the form 104s in the book. The calculator solution for Hc was usually within about 0.5' of that shown in the book.
An exception was fix 9.8 on page 239, which differed by 0.8 nm according to the calculator (which gave Ho=9°26.0'). Part of the difference is due to rounding errors in using table T21, but interpolating for minutes of declination directly would only reduce the error by about 0.3', hardly worth it in practice.
In many cases, the calculated azimuth (rounded to a whole degree) differed by 1° from that shown in the book. I think this occurred because the azimuth wasn't corrected for minutes of declination (although the section in Pub 249 on use of the tables remarks that "in general [Z] need not be interpolated for declination").
Anyway, that was a long story when all I really intended to say is that the hand written 'nines' in the book look very like 'fours' to me. Beware! If you look carefully, the hand written fours are clearly different to the nines.
Regards,
Lance Cowled
From: Hobart, Australia
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