substantially nullified application_number US 57756295 A description referring now to the drawings and first particularly to fig1 thereof there is shown therein a device 1 for measuring rotation angle errors including a driven pulley 2 connected to a drive motor 3 and a non driven pulley 4 connected to a rotation angle sensor 5 which transmits a rotation angle signal represented by the arrow associated therewith extending around the driven pulley 2 and the non driven pulley 4 is a drive belt 6 to be tested the inner side of the drive belt 6 forming a contact surface 7 adjacent to the drive belt 6 is a position sensor 8 which delivers a trigger pulse when a marking 9 provided on the outside of the drive belt 6 passes the position sensor 8 the rotation angle signal and the trigger pulse are supplied to an evaluation device 10 which computes therefrom the rotation angle error of the drive belt 6 i e the angular deviation of the rotational movement of the non driven pulley 4 from a uniform rotational movement of the driven pulley 2 the rotation angle error can be displayed as a curve and according to the magnitude and according to the phase position thereof with respect to the mark 9 respectively the principal cause of the rotation angle error becomes apparent from fig2 a 2b and 2c which show the positions of strands 11 in a drive belt 6 in.