is fixed the drive motor 23 has a spindle not shown to which the tool bit 22 is mounted the drive motor 23 selectively drives rotation of the tool bit 22 to work on the workpiece the cylindrical housing 21 is movably received in the interior space of the surrounding wall 12 to selectively move the motor 23 and the tool bit 22 with respect to the base assembly 1 the read out system 3 comprises an electrical circuit comprising a position sensor indicated at 31 a in fig5 31 b in fig1 a processing device not shown a display device 32 that comprises a liquid crystal display lcd in the embodiment illustrated but may be other known displaying devices such as a light emitting diode led based display a reset switch 33 for resetting data displayed on the display device 32 to zero and a mode switch 35 for switching between for example an english or metric units read out the read out system 3 is powered by for example a built in power source which may comprise one or more batteries either primary or secondary or an external ac power from an electrical main through an ac dc.