Thousands of box sextants have been made, sold and used by voyagers, over more than one hundred years. I am right-handed, need reading glasses, and have a right master eye. To read or set an old style box sextant at sea or airborne, try this:
1. Sit braced, arms free. Hold the open sextant in the left hand, scale uppermost, thumb underneath pointing right, second, third and little fingers cupping the sextant over the top, pointing right. The index finger is free.
2. Set the built- in magnifying glass over the vernier, about one inch from the scale. Bring the left hand up so the third bone from the tip presses on the tip of your nose. The right eye, magnifying glass and vernier are now lined up, and steady.
3. If necessary, adjust the focus with the right index finger, whatever eye glasses you may or may not wear. It may help to face so that light comes from the side, rather than overhead.
4. Read , and record the reading using the right hand, and a knee pad or cuff over the left fore-arm.
If you need to control a tiller or airplane stick with the left hand whilst reading or recording, use the three smallest fingers and heel of the hand for the control, and hold the sextant with the thumb and index finger. It will be necessary to move the head down to the sextant, rather than the sextant up to the head.