Hi
i have been given a Cooke
sextant. I am not sure it works correctly, (or maybe it's me!). the problem is this: with the
arc and micrometer both set to zero, when i look at the sun (with shades), i can adjust the side error and index error screws (both located on the horizon mirror) so that both suns appear on top of each other. however, when i simply move the
sextant to look at the distant horizon, there is clearly a lot of index error present as the right half of the horizon is far higher than the left half. similarly, if i then adjust the two screws on the horizon mirror whilst looking at the horizon, and get the horizon object perfectly aligned (eg: to a distant light house), with no side/index error, but then look at the sun, the two suns (through index and horizon mirrors) are way out. i wonder what type of error this is?