bit 20 out from the curved section 16 of the guide channel into the coal formation 11 drill bit 20 advances outwardly from curved section 16 of the guide channel to form a small borehole 38 fig2 the controlled length of lower cables 29 extending through sleeve segments 17 assures that there is no slack between sleeve segments 17 which extend beyond housing 13 thus assuring that borehole 38 is a straight hole continuing upwardly from curved guide channel 16 upon drill bit 20 reaching the position shown in fig2 where it contacts the hard rock formation 12 the torque on motor 14 will increase to the point where reversing switch 37 is tripped and motor 14 will then move in the opposite direction drawing drill bit 20 back into the end of curved guide channel 16 to the position shown in fig1 upon reaching the starting position contact switch 36 and reversing switch 37 are tripped by the motor frame such that the motor is placed in the forward mode and the power to the motor is shut down the unit is then ready for removal from the long hole or for drilling another small diameter hole from long hole 10 to rock formation 12 it is a relatively simple matter to determine how far the unit advanced during a cycle thus enabling the operator to determine how far bit 20 advanced out of guide channel 16 thus indicating the distance between the top of long hole 10 and the overlying rock formation 12 it will be apparent that by rotating the entire unit 180 u00b0 the distance from the bottom of long hole 10 to an underlying rock formation could similarly be.