These were used in the horizontal orientation by the Army in WW1 to assist gun aiming (rather than for the conventional Naval use of determing position from the time and the sun's position at noon).
There are cheap Indian knock-off versions freely available on EBay, but genuine items such as this one are rather fewer in number and fetch rather more.
Pocket Sextant by John Liddle, on Flickr
There are cheap Indian knock-off versions freely available on EBay, but genuine items such as this one are rather fewer in number and fetch rather more.
Pocket Sextant by John Liddle, on Flickr
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