Abstract: The process consists of pre-positioning conserving a reversible counter with memory (9) in the maximum state, counting the positive pulses in such state, receiving and counting the positive pulses with respect to a predetermined basic step to derive a number expressed in units of basic step, transmitting this number to at least one priority interrupt terminal (13) of a microprocessor (14); emitting a reference time frequency, measuring the time lapsed between the appearance of two successive pulses presenting themselves at at least the interrupt terminal (13), determining the ratio between the lapsed time and the number expressed in units of basic step, transmitting this ratio to the microprocessor (14) and displaying it, and controlling the advance of an element enabling graphic display of the speed of translation of the rotating or percussive member with respect to its dimension of penetration, this speed of translation of the member being an instantaneous speed of advance.