NavList:

Lu,

As you say the typical slide rule leaves a little bit to be desired when performing Hc sight reduction but it should still be in the navigators kit. To name a few of my favorite slide rule calculations: azimuth of body, ex-meridian by formula, horizontal angle circle radius, time speed distance, and ETA.

Greg Rudzinski

[NavList] Re: Bowditch sightreduction table (Ageton?)
From: Lu Abel
Date: 7 Apr 2012 17:12
Re slide rules: You need five or six-place accuracy in LOC calculations to get a reasonable Hc and the commonplace that all of engineers (of sufficient age, at least) learned on were accurate to about 2-1/2 places. This list has discussed rules such as the Bygrave that appears to have much more accuracy. My view, though, is that slide rules, while useful for almost all engineering calculations (anybody want even a 1% margin of error on safety calculations?), celestial requires calculations 1000 more times accurate. High-precision slide rules might offer one solution, but there are others, eg, the various sight reduction tables that have been published over the ages.

Let's not forget that before WW II, "calculator" meant a person who did calculations, not a machine (mechanical or electronic) for doing them. So I suspect that many of our older sight reduction tables were produced by a roomful of "calculators" tediously working out a five- or six-place solution to just one entry in the table.

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