This is the instrument used to mark the location of various points on the map; the cellarhole, the unmarked roads, intersections and Nahum Green's Monument.

The photo shows the instrument hanging from the back of the Monument and is displaying the exact coordinates, longitude and latitude, of the stone.

This global positioning system unit is simply referred to as a GPS unit. Accurate to within 50 feet it is, interestingly, the same type of sophisticated electronic device used by U.S. Military craft and Special Forces to accurately pinpoint targets.

It has many practical civilian uses including piloting of private and commercial aircraft, commercial fishing and pleasure craft. It is also used by engineers, cartographers, woodsman, hunters and hikers alike.

Technically, it is a specialized radio receiver which homes in on overhead satellites. When it locks on to three overhead satellites it displays longitude and latitude. Locking in a fourth satellite, will show elevation.