will be seen that the absolute pressure in the region 126 is higher than in the region 124 indicating that the motor 36 is under load which is what one would expect when the motor 36 goes from idling to under load in the event the coiled tubing 34 is lowered too rapidly the pump pressure rises as at 128 suggesting an imminent stalling of the motor 36 at this time the coiled tubing operator would manipulate the injection head 44 to either quit lowering the coiled tubing 34 or raise the coiled tubing 34 to quit drilling the pressure necessary to stall a motor 36 of the type used on coiled tubing units 32 varies somewhat but a 200 psi pressure rise would be sufficient in many cases to stall the motor such a pressure rise is well below the fluctuations inherent in a high pressure multiplex pump so it would be completely masked to the coiled tubing unit operator in one aspect of this invention the differential pressure is displayed in box 110 or a trace 130 of differential pressure is provided to assist in detecting an incipient stall of the motor 34 the differential pressure displayed in box 110 or the trace 130 is a pressure differential p 2 u2212 p 1 where p 1 is the pressure when the motor 36 is idling and p 2 is the instantaneous pressure of the motor 36 to set the differential pressure trace 130 and to zero the instantaneous pressure differential shown in box the user input 90 shown as a depressible button in fig5 and 6 is depressed at a time when.