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Bruce,

Arc Sin [ Sin Dec/Sin Lat] = Prime Vertical

Useful for determining if 180° or 0° will be used for Z value when using formula Z = Arc Sin [ (Cos Dec)(Sin t)/Cos Hc]

Also useful for the most accurate time to take a time sight observation. 

If the regular azimuth intercept method is used then the observation azimuth need not be plotted since the azimuth is either due east or west. 

Greg Rudzinski

From: Bruce J. Pennino
Date: 2016 Jun 5, 17:34 -0700

Hello:

I have not done any CN for at least  6 months.So a couple of days ago I went to a spot with my Astra and took some shots. I had made up my mind I would reduce the sight by HO 249, Weens 1927, and HO 208...see how much I'd forgotten. Because I was sighting to the west, I even had my "trusty" WW ll army surplus compass (probably used too close to car). The compass results indicated the sun at 270 +/- (true). I've always liked Weens for Hc and calculated the Z with his tables. BUT I could not quickly make sense of his quadrant rules. HO 249 works "like a charm". The bearing was about 260 true. HO 208 also was no problem with quadrant identification.  I then realized that by calculating the PV  angle it would immediately be obvious if I was sighting to SW or NW,ie,Ho greater than PV then sighting to SW; Ho less than PV sighting to NW for this time of year at this latitude.

Any other uses for PV?

Bruce