I worked in industrial automation controls for a while. There they used a concept called quadrature to determine servo movement precisely. Quadrature is basically a grey code of [00, 01, 11, 10] that is repeated. You know what direction you are going by where you are and what comes next. If you are on 01 and see 00 you know you are going left. If you are on 01 and see 11 then you are going right.

With a tad bit of math involving the gear box attached to the servo you know that one tick is real world distance X. From there it is a matter of establishing a "home" position, and counting your ticks as you move.