NavList:

George H, you wrote:
"The original purpose of the backsight, in which the horizon was viewed in the
opposite direction (and was never, as far as I know, used with a telescope) was to allow a lunar, greater than 90º, to be measured with an octant."

I've never heard that before, and considering the great difficulty in getting an index correction for the back sight, which you described very clearly, it seems unlikely. So do you have a source for this? Do you remember where you encountered this idea that back sights were originally for lunars?

-FER

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