NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2010 Mar 24, 11:34 -0700
Scott,
An additional thing to think about as you are shooting through glass at the far shore of a lake is sextant parallax (roughly determined by calculating the inverse tangent of the distance from the index mirror center to the center of the scope objective divided by the distance to the viewed horizon). On my Tamaya Jupiter this works out to inverse tan 2.2 inches divided by 7200 inches = 1.0 minutes of arc for a shore line 200 yards away. The parallax will be observed as off the arc and therefore added to the observed altitude (Hs). How far is your lake horizon and what model of sextant do you have?
GRuzinski
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