A two number value is used to plot a course. The direction of flight, of the ship, is always the starting point, for a measurement, and the distance doesn't matter. The first digits are called "bearing", and they give the horizontal angle, towards an object. The second digits are called "mark", and they give the vertical angle, towards an object. Combine those two sets of digits, and you have the position of the object, in 3-dimensional space.