# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Ex-Meridian Exercise**

**From:**George Huxtable

**Date:**2011 Jan 7, 23:27 -0000

Thanks to Gary for correcting my error, as follows- "The formula given for table 29 of Bowditch is: a = 1.9635" cos L cos d csc (L ~ d)" ================== I had written- "It's given as A = 1.9635" x cos lat cos dec / sin (lat - dec) because sin (lat - dec) = cos alt, this becomes A = 1.9635" x cos lat cos dec / sec alt, in which the trig quantities exactly correspond with those on the slide rule." But of course that division sign should not have been there. It had crept by my accident, and I should have written the result as- "A = 1.9635" x cos lat cos dec sec alt, in which the trig quantities exactly correspond with those on the slide rule" which would then be in agreement with Gary, and Bowditch. And then, with altered units, of time in degrees of hour angle, rather than minutes-of-time, and of correction in arc-minutes rather than arc-seconds, this would correspond with the equation of Ronald's slide-rule Sorry. ============== Incidentally, a simple "minus" sign can be used in place of the ~ sign to be found in Bowditch, as long as the simple convention of North is positive, South is negative is adopted for latitudes and declinations. George. contact George Huxtable, at george{at}hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.