NavList:

David Pike, please read my 10 November post again, especially the words in the following two sentences with the phrase scope line of sight (this instrument was not designed to only use the scope with the upper horizon mirror):

“To use the upper horizon mirror, align the scope line of sight with it and tip the quintant up 5 degrees for a horizontal view.”

“To use the lower horizon mirror align the scope line of sight with it and tip the quintant up 25 degrees for a horizontal view.”

This instrument is designed such that both the upper horizon mirror and index mirror angles are at, or very close to, 69 degrees (relative to a line joining like points on the arc extremities) when the index arm is set to 0.   The scope mount is positioned higher than the center of the upper horizon mirror such that its line of sight is depressed 5 degrees below horizontal, under the conditions of the previous sentence. In use, raising the line of sight to horizontal increases both the horizon mirror angle and index mirror angle by 5 degrees to 74 degrees when the index arm is set to 0.

In like manner, when using the scope with the lower horizon mirror the initial line of sight is depressed 25 degrees, the horizon mirror angle is 49 degrees, and the index mirror angle is 69 degrees. Raising the line of sight 25 degrees for a horizontal sight increases the horizon mirror angle to 74 degrees and the index mirror angle to 94 degrees.

In light of the above, if it’s not clear that both of your proof statements (a. and b.) are incorrect, we can discuss this--or any other aspect of this, or other designs--further.

Chuck V.