Compasses

Compasses are used for navigation and route finding. They have magnetized needles that align to point to the earth’s magnetic north. To obtain true north a correction, called declination, is required as magnetic north is not in the same location as true north and it constantly changes position.

The surveyor’s compass or “circumferentor,” as it was called in Europe, was the primary instrument used for determining direction for surveying until the late 19th century, when surveyors started to use astronomic observations for determining direction.

Because of compasses magnetic attraction surveyors nowdays often use them to locate buried metal survey monuments. Also, in the past objects (bearing trees, iron bars, etc.) were used to reference survey monuments. As they were often referenced by distance and magnetic direction, compasses are used for restoration work.