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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2026 Aug 10, 15:51 -0700
Frank Reed You wrote: "My guess --only a guess-- is something more mundane about calculation. The secant function was fundamentally a construct of the era of manual calculation. If you need to divide by the cosine of some angle, in logarithms that's equivalent to subtracting a logcos value, or it's equivalent to adding a logsec value. Adding is easier and less prone to error than subtraction. That made the logsec, and in other computations the logcsc, valuable on practical grounds. Now they are antiques, all but forgotten."
Frank
You are probably correct. I'd not thought of that. I tried all three ways using Dec20N Lat 53N. I got the same answer each time, but it was a struggle to remember what to do with those bar ones and nines. I gave up on the nines.
Jaquelin Hardy. I didn’t realise Jaquelin could be a boy or a girl name, so apologies if I got it wrong. On age, I had a little CBM hand-held around 1971/72, so I’ll drop your age to around 76. DaveP
