NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Norm Goldblatt
Date: 2013 May 9, 13:26 -0700
Randall. It looks like you have a mirrored surface on the bottom of the glass. If you take the reflection from that surface, there will be a small error due to the non-parallelism of top and bottom surfaces of mirror. Turns out it's about 2 times the wedge angle. For float glass, an affordable flat substrate, the specs are parallelism of less than 30 sec. For a wedge angle of 10 sec, the reflected image will be displaced by 20 sec, up, down, or lateral or a bit of both, depending on the direction of the wedge. Maybe there are other uncertainties larger than this, but since you mentioned the precision of levels being 10 sec, thought I'd ask if wedge was considered.
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