he resets the second function 2 enter from the bottom of the excavation and then begins to excavate the slope until he reads 15 percent positive on the display 51 and he keeps this pitch until he reaches the ground level above the hole referring now to fig5 of the drawings there is shown the flow chart of the program for inputting information in the memory of the computer and the execution of the calculation and displays referring to the steps of the flow chart and as shown at step 60 the boom lengths are measured as above described and the data is entered into the computer by the keyboard 50 the step of automatic feeding the data from the sensors 25 and 25 u2032 is expressed by steps 61 and 62 all of this data is inserted in a conversion function of the system illustrated at step 63 in the computer these values are then displayed on the screen 48 as expressed by step 64 also the data conversion step 63 then feeds signals to computer circuitry which effectuates the mathematical treatment of the information signals as exemplified by step 65 and the resultant signals representative of the absolute height value are obtained in step 66 and absolute flow value in step 67 these values are processed in step 68 in relation to a virtual zero setting signal as entered into the memory of the computer by the operator and representative at step 69 the computer then calculates the vectorial slope angle between active position and the virtual zero signal in step 70.