[header] How to use a sextant [title] Know, if possible, your position above sea level. [step] If you're not using the sextant from aboard a ship at sea, you'll have to correct your sighting for your height above sea level. We'll discuss the correction later; for now, you just need to know your elevation above sea level. 
[title] Sight the horizon by looking through the horizon mirror. [step] The horizon mirror is only partially silvered, allowing you to look through it and through the sighting scope beyond it.