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Brian,

I can't remember the origins of the ex-meridian formula using the .5235 constant :(  The other major difference is the division by Cos Altitude vs. Sin(Lat+/-Dec). 

Greg Rudzinski

From: Brian Walton
Date: 2019 Mar 8, 06:11 -0800

Greg,

   Thank you for your quick reply.  It seems that an all hav ex- meridian calculation is just as troublesome as doing a normal all hav intercept Hc.  Your handwriting indicates you feel the same?

   I am still horizontal with ‘flu, but a glance at MoB tables suggests a rule of thumb.  If within 4 minutes, ignore the correction:  if between 4 and 8 mins, add 1’ per minute time, and if over 12 mins, do a St Hilaire all hav Hc.

   I’m talking mid-ocean, solo, with a frayed forestay and leaking bilge, not surveying the Spratleys for the latest airfield.  

   I still cannot see how you get from 1.9635 to .5235.  Perhaps I’d better have another sloe gin and Paracetomol before the theorists get me,

Brian