Proa

  When we want the exact position of a circular motion, or any other movment can be converted to circular, we use absolut encoder.

Every moment gives us the exact location of the degree found with the accuracy we want.

A disc with many concentric lines as removed from the center and become smaller in length is the basic design of such an encoder.

A light from one side of the disc and a detector on the other make it possible to detect the position.

Eg If you "see" the first three marks from the center out to be 0 by being transparent, light passes, we are somewhere between 0 and 45 degrees. 

Each of the next sign we restrict the degrees in half.