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What Are the Elements of a Compass?

Compasses are navigational tools that allow hikers and explorers to find their way in the wilderness by pointing the way to magnetic north; these tools come in a variety of different formats. More expensive and more complicated models have advanced features. All compasses, however, have the same basic elements that allow the devices to point the way to magnetic north. Compasses measure the geographic distance between two points. These instruments work via magnets, which pivot in response to the Earth's magnetic field.

Base and Magnetic Needle
- These two elements are essential to the operation of every compass. The baseplate is a hard, flat, round surface upon which all other elements are mounted. Some baseplates have rulers or a protractor on the edge that may be used for measuring distances on a map. The direction-of-travel arrow is located on the baseplate. The magnetic needle has one end painted red that always points to the north due to the Earth's magnetic field. The needle is mounted on a bearing that allows it to rotate freely.
Housing
- All moving parts of a compass are located within the housing, which is often filled with water to suspend the magnetic needle. Included in the housing is a revolving dial that shows the cardinal points --- minimally north, south, east and west --- as well as degrees from 0 to 360. Compasses also typically mark the half cardinal points, or the directions halfway between each cardinal point. A compass operates by rotating the housing so the magnetic needle lines up with the orienting arrow when taking a bearing. The crystal, which is either flat or beveled, covers the housing.
Orienting Marks
- The north-south orienting arrow on the housing floor is outlined in red or black. This element is used to align the magnetic needle when taking a bearing and is essential in setting a compass for magnetic declination. Orienting lines are a series of parallel lines, located either on the housing floor or the baseplate. These lines are used to line up the compass dial with grid lines on a map. Orienting lines and the orienting arrow are used to determine the angle of declination, also known as the difference between geographic and magnetic north.
Less Common Elements
- Older compasses, as well as more expensive models or those used for specialty work, may have additional elements. The variation marking found on older compasses is used to determine declination. More expensive compasses have a transit lock that lifts the needle off of its pivot and minimizes wear. A magnifying lens may help show tiny symbols and features on maps, while a sighting mirror may improve accuracy when reading bearings.

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