A compass consists of a magnitized steel needle mounted on a pivot at the center or a graduated circle. Unless disturbed by a local attraction, the needle aligns itself with the earth's magnetic field and points toward magnetic north (in the northern hemisphere). […] The compass has been used by navigators and others for many centuries to determine directions. Prior to the invention of the transit, a compass furnished surveyors with the most practical way to measure horizontal angles and directions of lines.