NavList:

Brad, you wrote:
"In the octants/quadrants I have looked at, there very much seems to be a peep sight for backsights, just as there is a special backsight mirror. Your eye is forced into location. This is similar to the arrangement for a foresight observation, albeit that the peep and mirrors are in different locations."

The problem, Brad, is "collimation". The line of sight has to remain parallel to the frame. You can judge this by eyeball to some extent. Just line everything up in the middle of the field of view. Also, any mis-collimation will show up as a change in separation across the field of view (just like the check for telescope collimation that you're familiar with from an old Bowditch). So you can do a little side-to-side rocking motion and find the minimum angle. Since swinging the arc relative to the horizon is also a search for minimum angle, you can combine these two motions in a general yawing and pitching motion (if you've ever played with a Bris sextant, it's just the same thing).

-FER

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