Compass

Long before GPS satellites and other electronic navigational aids, the compass gave humans an easy and inexpensive way to orient themselves. A compass is a lightly magnetized needle that, when allowed to move freely, points in direction of magnetic north, giving the user a reference point for measuring all other directions. A compass allows the user to determine direction, take bearings and plot a route of travel on a map.

Compass Features

The main features of a standard compass are displayed below:

Baseplate

The flat surface on which the rest of the compass is mounted. It includes a ruler on its edges for measuring distances on maps.

Dial

A circular, rotating bezel ring around the compass housing, marked with degrees.

Direction of Travel Arrow

This arrow is marked on the base plate, parallel to the sides of the base plate. It shows the bearing the user is taking or the direction of travel.

Housing

A round plastic container filled with liquid containing the magnetic needle.

Index Pointer

This is fixed on the outer edge of the compass housing as an extension of the direction of travel arrow. When the compass housing is rotated, the index pointer will mark the set bearing.

Magnifier

Useful for seeing small map features.

Needle

A magnetised piece of metal that has one end coloured red to indicate magnetic north. It sits inside a fluid-filled capsule on a fine point so it can rotate freely when the compass is held level and steady. The fluid causes the needle to stop quickly rather than oscillate back and forth around magnetic north.

Orienting Arrow

A fixed arrow marked on the floor of the housing, aligned to north. It rotates with the housing when the dial is turned.

Orienting Lines

A series of parallel lines marked on the floor of the housing to be aligned with the eastings (the line that run north to south) on a map. In some compasses, half of each line is coloured red to indicate north.

Scales

Displayed along the edge of the base plate to enable the user to measure distances with different map scales.