are mounted in the box 22 and are switched closed to allow current to pass through permitting the first inclination detector means 12 to operate upon the boom being in its normal orientation and when the boom 15 is rotated 180 u00b0 to switch open thus disabling the first detector means 12 the 30 sensors 32 a and 34a are similarly mounted in the box 22 and performs to same task with respect to the second inclination detector means 12a as may readily be observed the invention may be limitedly practiced with only one inclination detector means 12 without the sensor devices 32 34 32a and 34a when the boom 15 is not rotated with directed electrical connection from the switching devise 18 and 20 to the read out means 28 and 30 respectively multiple sensors 34 and 34a are utilized to isolate the respective poriton of the circuit and prevent electrical feedback through other portions of the circuit and possibly obtaining false readings during operation of the bore hole drill assembly 14 fig4 6 in its normal mode with the boom 15 in its normal mode the sensor devices 32 and 34 would energize the first inclination detector means 12 with the sensor devices 32a and 34a de energizing the second inclination detector means 12a the boom 15 would be elevated to angle u03b8 until the switching device 18 closed thus permitting an electrical signal to pass to the first read.