Celestial navigation exploits the principle that every measurement taken with a sextant converts to a line of position on a chart, the intersections of two or more such lines providing a position fix.
1 - Set Assumed Position
2 - Sight Preparation
Tap MODE in the action bar to toggle a view of the computed horizon at the assumed position
3 - Add a Sight
Open the Sights Table by tapping the icon at the bottom right of the screen.
4 - Lines of Position
5 - Sight Reduction Detail
Select a table entry and tap altitude