To use a sextant to find the angle of elevation of an object, you’ll need to know your elevation above sea level. Sight the horizon by looking through the horizon mirror, then move the sextant’s index arm until the object you’re trying to find is also visible on the horizon. Clamp the index arm in place with the flip-lock, then turn the micrometer knob to fine-tune the sextant so the object is perfectly aligned with the horizon. Record the time you made your sighting in hours, minutes, and seconds, then record the angle measure, which you can find on the index bar, and correct for your elevation if necessary.