Traditional Navigation.

This is a sextant, a device used for many hundreds of years to navigate ships across oceans. Until 20 years ago, it was still the most reliable way to find one's position anywhere at sea. Navigation by satellite has become far more precise and and few modern sailors choose to learn celestial navigation.

A sextant is merely a precision measuring device, which can provide the user with mathematical information. By measuring the angle of the sun's height above the horizon at a specific time of day, for example at exactly the stroke of midday, tables can be used to calculate the position of a circle on the earth's surface. The navigator then knows he is somewhere on that circle.

By taking two more 'sights', two more circles can be drawn. Those three circles will intersect in two places. The navigator then knows he is in either one or the other of those intersections. Providing he knows whether he is in the northern or southern hemisphere, an accurate position is easy to determine.

It is quite simple in fact. Anyone who enjoys a mathematical challenge would enjoy sextant navigation.