All aircraft must have a magnetic compass that tells you which way you’re going relative to magnetic north. However, if you’ve ever used a compass you know that it has many inherent problems. It has lots of drift and slop, swinging back and forth before it settles down; especially in a vehicle that’s turning, climbing, and descending. It also is affected by nearby magnetic fields, such as the electronic gear in your plane. Airplane compasses have deviation charts on them to help you adjust for these problems, but the best solution is a heading indicator, a gyroscopic instrument that is more stable and easier to read than a compass.
With an image of a small aircraft in the center, a heading indicator is easier to interpret, showing you which way you are headed and the plane’s relationship to other points on the compass. Many heading indicators have rotating markers that can be moved around the perimeter to help you remember which direction you’re supposed to be going, called your heading.
Because a heading indicator is not a compass but a gyroscope, it needs to be manually adjusted (typically about every 15 minutes) to reflect the compass reading. Of course, you should make this adjustment only in straight-and-level flight when the compass is stabilized and not wobbling around.
"Man cannot discover new oceans unless he has the courage to lose sight of the shore."
-- Andre Gide