the algorithm moves forward to step 226 to monitor this rise which is graphically demonstrated in fig1 as point c fig1 shows a coordinate graph illustrating both a pressure versus displacement waveform for comparison and a velocity waveform for a rivet set with the algorithm proceeding next to step 228 the velocity waveform is monitored until point d is found point d is the point where the mandrel head has reached the secondary side of the application the difference between point c and point d determines whether secondary head formation or clamp is correct the correctness of this difference is determined by using the comparator circuit which compares the value derived from the set with the predetermined desired value stored in the programmable reference 114 at step 230 the difference between points c and d measured along the y axis is determined and this difference is compared against a predetermined range for an ideal difference a correct set is illustrated in fig1 a which is a sectional view of a workpiece comprising two plates labeled c and d held together by a rivet r with this correct set being identified at step 232 the green light 116 is illuminated fig1 is a graph similar to that of fig1 but illustrating a waveform in which the difference between points c and d is considerably less than that between points c and d of fig1 this small difference is not enough to constitute a good clamp situation the resulting bad clamp is demonstrated in a sectional view in fig1 a illustrating a rivet r 39 fastening together two plates c and d this type of bad clamp typically indicates an overgrip situation as the air.