the break point for a flat contour head is sharply defined by the dropout of all signal including noise when the wrap angle is reduced below a functional threshold for the head to establish a critical point or trigger point from which the correct adjustment of the position of the roller is determined the next step in the adjustment process is preferably to rotate the eccentric shaft a predetermined amount which is either a constant or more accurately is a variable value which is obtained by table lookup using the angle of the break point to find the amount by which the shaft should be rotated for example the optimum wrap angle may be obtained when the eccentric shaft is rotated theta degrees from the break point to move the roller back away from the head if the eccentric shaft is rotated in one direction to find the break point then it will be rotated in the reverse direction to achieve the correct break angle the amount of the rotation needed may be different for the roller on the first side of the head than on the second side if a table is used then there must be way for the operator to read an angle corresponding to the break point the adjustment tool described below can aid in obtaining this value for heads having a radius of curvature that is too small for the previously described method to work which will be referred to herein as u201c convex heads u201d it is preferable to use the amplitude of a signal generated by the moving tape to make the adjustment the signal may be noise from the tape the servo signal or a specially recorded signal for the adjustment procedure as indicated above there may be many choices.