Aeronautical charts include this information. Terms are "true north" which is based on lat/long grid, and "magnetic north". An airplane has a magnetic compass a

Aeronautical charts include this information. Terms are "true north" which is based on lat/long grid, and "magnetic north". An airplane has a magnetic compass as the primary reference, but it's a little wobbly, so on the ground prior to departure, a gyroscopic compass (called a heading indicator, directional gyro) is set to match the magnetic compass. If you do a some steep turns, or many shallower ones, you can get your heading indicator to drift. And if you travel some distance east or west it'll also drift relative to the magnetic compass, so you have to reset them to match periodically. The magenta dashed line going from top to bottom at a slight angle on the left of this image indicates degrees magnetic declination. https://www.faa.gov/air_traffic/flight_info/aeronav/media/VFRCarib.jpg https://www.faa.gov/air_traffic/flight_info/aeronav/media/VF...