Kinds of Compasses

For centuries, travelers have used compasses to find their way, whether orienteering on land or on open water. They have been changed over time, starting with magnetic compasses in wood or ivory casings and now commonly through GPS units installed in automobiles. Several different types of compasses exist, including the protractor, thumb, magnetic, gyro and astrocompass. Each is used for a unique purpose; some determine magnetic north and others true north.

  1. Baseplate or Protractor Compass

    • Invented by the Kjellstrom brothers, this compass has a rectangular baseplate with a rotating compass housing marked in degrees. The floor of the compass housing is marked with lines running parallel to an arrow. These compasses may also have scale bars for measuring map distances on an edge of the baseplate, a magnifying glass for deciphering map detail, and templates for marking orienteering courses.

    Thumb Compass

    • Developed as an alternative to the baseplate compass, the thumb compass was made with a strap used to attach the compass to the thumb. Designed by a Swedish orienteer, this compass is placed on the thumb of the hand and is used to hold it on the map. The compass and map are therefore read together, allowing for quicker and easier map reading, while leaving one hand free.

    Magnetic Compass

    • The most commonly used compass is the magnetic compass. It determines magnetic north through magnetized iron or steel set in low friction so that it can move freely. Mariners have long used a version of this compass, with cases made of wood or ivory. A stone, whose magnetic property had been discovered centuries before in China, was used to magnetize the needle. It was called a lodestone after the seaman's lodestar, which guided ships at sea. Brass casings were later used as they do not affect the needle. By the 16th century, it had been improved to the point that it is was similar to those used today.

    Gyro compass

    • Developed in the 19th century, this compass contains a wheel or ball, which spins at high speeds and uses the earth's spinning axis along with the law of conservation of angular momentum to point to true north. The gyro compass is often used by large ships in need of accurately predicting true north.

    Astrocompass

    • This compass also determines true north rather than magnetic north. It is used primarily in areas such as the far north and south poles, where magnetic compasses are faulty and gyro compasses do not work. An astrocompass uses the locations of stars and planets to find true north and requires accurate information about the time and date as well as longitude and latitude.

    GPS compass

    • GPS compasses use satellites in orbit over the earth to determine location. Drivers and hikers use these compasses often, but ships and the military continue to use the gyro compass or magnetic compass when GPS compasses are unable to retrieve enough information via satellite.