1. IN AN OILFIELD DRILLING UNIT INCLUDING AS WORKING MEMBERS A STRING OF DRILL PIPE WHICH IS ROTATED TO ADVANCE A DRILL BIT INTO THE EARTH AND A HOISTING LINE BY MEANS OF WHICH SAID STRING OF PIPE IS RAISED AND LOWERED IN THE BOREHOLE, THE IMPROVEMENT WHICH COMPRISES: FIRST MEANS FOR MEASURING THE FORCE APPLIED TO ONE OF SAID WORKING MEMBERS OF SAID DRILLING UNIT AND OBTAINING AN OUTPUT PROPORTIONAL TO THE FORCE THUS MEASURED; SECOND MEANS RESPONSIVE TO THE MOVEMENT OF SAID WORKING MEMBER FOR OBTAINING AN OUTPUT PROPORTIONAL TO THE MOVEMENT OF SAID WORKING MEMBER; INTEGRATING MEANS FOR OBTAINING THE SUMMATION OF THE PRODUCT OF A FIRST INPUT AND A SECOND INPUT; THIRD MEANS FOR APPLYING THE OUTPUT OF SAID FIRST MEANS TO SAID INTEGRATING MEANS AS SAID FIRST INPUT; FOURTH MEANS FOR APPLYING THE OUTPUT OF SAID SECOND MEANS TO SAID INTEGRATING MEANS AS SAID SECOND INPUT.