How your dashboard compass works will depend on the type of compass you purchase. A magnetic compass is comprised of a lightweight, small magnet that pivots on a near frictionless point. One end of the needle is marked to indicate North; the area surrounding the compass will usually have numerical markings allowing to determine degrees away from North. These are not the best types of compass for your vehicle.
More commonly found in vehicles are floating compasses or ball compasses. In this type of compass, the ball or needle floats freely on a liquid, usually a light oil. The needle or ball then rotates to indicate North depending on magnetic attraction.
Digital compasses are more complex in their design. Such compasses use magnetic sensor technology that can sense differences in the earth’s magnetic field electronically. It can sense the difference between the earth’s magnetic field and other magnetic disturbances, such as that created by the electrical systems in your vehicle.