Compasses and magnetometers provide continuous heading and magnetic field information. A compass is used to determine direction and often consists of a magnetic needle or needles horizontally mounted or suspended, and which are free to pivot until aligned with the earth's magnetic field. A magnetometer is used to measure the direction and/or intensity of magnetic fields. Specifications for compasses and magnetometers include type, technology, capabilities, and applications.

There are many different types of compasses and magnetometers. A variation compass is used by observing the variations of a needle. A gyrocompass or astrocompass can also be used to find "true north". Typically, combination compasses and magnetometers are also used in navigation applications. There are several basic types of magnetometers. A fluxgate magnetometer is based on a magnetic saturation circuit. A proton magnetometer is a device used in subsurface detection which records variation in the earth's magnetic field. A vector magnetometer can measure a component of a magnetic field in a particular direction. There are also several types of compasses.

Compasses and magnetometers differ in terms of capabilities. A fluxgate magnetometer is capable of measuring the strength of any component of the Earth's magnetic field by reorienting the instrument so that its cores are parallel to the desired component. Some fluxgate magnetometers are capable of measurements in the range 0.5 to 1.0 nTesla. Proton magnetometers measure the total magnetic field with an accuracy of ca 1 nTesla or better. A proton magnetometer is often used for ground measurements in slow-moving vehicles, or for marine measurements. A vector magnetometer defines magnetic field strength, inclination, and declination. There are several basic types of compensated pitch/roll compass/magnetometer systems. Examples include general-purpose, geophysical-vertical, and geophysical-horizontal compass/magnetometer systems.

Compasses and magnetometers are used in applications that require precise orientation, navigation, and leveling information. For example, combination compasses and magnetometers are used on satellites and aboard airplanes that map the local structure of the Earth's magnetic field. Navies use compasses and magnetometers to detect submarines under water. Surveyors can use these magnetometers to locate boundary stakes buried in the ground or hidden by vegetation.