From: Robert Swartz
Date: 2016 Dec 30, 23:09 -0800
Living in an area w/ high light pollution (Chicago suburb), Venus provided an excellent point source light at an infinite distance for calibrating two marine sextants. After first checking perpendicularity of the index mirror, I took the two sextants down to Lake Michigan and used the natural horizon to get a gross coincident adjustnent of the horizon mirror. I then took them to my yard and, at my leisure, made final horizontal and vertical adjustments using Venus for image coincidence to remove index error.
The sextants were a Plath WWII German Kriegsmarine and a US Navy WWII David White.