Surveying compasses were used during colonial times to survey land, which requires the precise measurement of horizontal angles and distances. These devices contain a compass with a moving needle that indicates the north-south line, together with a pair of sights attached to a disc divided into 360 degrees, which rotates beneath the compass needle. The compass needle provides a fixed reference because it always points to magnetic north. An object can be viewed through the two sights and the angle between that object and magnetic north is then read off the graduated dial. Performing this measurement for two objects, such as boundary markers, allows you to calculate the angle between them. Surveying compasses were used together with measuring chains to create maps.
Most surveying compasses were made of brass, but wooden versions were common in New England during the 18th and 19th centuries. They were a bit less accurate than their brass counterparts but still got the job done. Surveying compasses were replaced by theodolites during the 19th century.