Why navigate, and dead reckoning from first principles

Air navigation is the practical art of getting an aeroplane from one place to another, safely and on time, knowing where you are throughout. Strip away the instruments and it comes down to four numbers per leg: the track you want to fly over the ground, the heading you must point the aeroplane at to achieve that track in the prevailing wind, the time the leg will take, and the fuel it will burn. Get those right and you arrive where you intended with reserves to spare.