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Here is another way to accomplish your goal. Get a small light and a small video spy camera, mine looks like a key fob and cost $25 at Fry's. Rubber band the camera on your index finger, (the light has a strip of velcro to hold it on,) of your left hand. Calibrate the clock in the camera by video recording a radio time signal or photograph your chronometer. Then take your sight, say "mark" which then is time stamped, and read out the sextant, using the video recorder as a simple audio recorder but with a precise time stamp. You can photograph the sextant at the same time so that you have a record if you want.

See the attached videos.

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