A service node is provided in a mobile communications network which collects radio link measurement reports which are transmitted to the service node by mobile stations. The movement of the rollers in relation to the frame of the printing unit is utilised in order, during the movement operation, to mechanically manoeuvre locking devices at the bearing housings of the rollers between open and closed position. The positioning string is retrieved leaving the tool wedgeably secured within the well bore for dispensing pressurized fluid within the well bore dislodging fluid and trapped foreign material within the horizontal leg of the well bore. A notice is provided to an operator when the counted number of operations of the device exceeds the established frequency indicating a need for a cleaning operation for the device.