priority unless the maximum rate of penetration is surpassed whereby plc 2 is programmed to then prevent further movement within a particular time interval or for a predetermined time period to thereby slow movement of the coiled tubing to the predetermined maximum rate the maximum rate of penetration may be predetermined based on testing and or other data size and type of pipe size of the mill and mill motor specifications and the like in this way the desired rate of penetration which the controller may be utilized to interpret as a desired number or encoder pulses per interval can be predetermined for input by the operator in another embodiment plc 2 may be programmed to prioritize rate of penetration by operating injector 5 to move coiled tubing 1 at a predetermined rate whereby if the weight on bit and or drilling fluid indicators stay within a preset range then the milling operation continues turning again to the figure there is also shown a bottom hole assembly 9 which after the casing milling has been completed is attached to the coiled tubing 1 and is used to drill a sidetrack wellbore 12 a distinct advantage of the control monitoring system of the present invention is that it serves as a backup to ensure greater penetration.