the reference plane at a reference level the laser receiver 60 is mounted along the pivot axis 16 where it will intersect the laser plane 32 substantially every time the bucket 14 is withdrawn from or inserted into a trench during the normal course of emptying a load of dirt from the bucket 14 at the instant the beam contacts the receiver the laser receiver will produce an output that is supplied to a microprocessor 70 mounted in the cab of the excavating machine the depth measuring sensor 40 and the inclination sensor 50 also provide outputs which are supplied to the microprocessor 70 such that at the very instant the laser receiver penetrates the laser plane the depth measuring sensor and inclination sensor are calibrated to a known reference level with respect to the grade stake 35 the depth sensor provides a signal to a depth sensor receiver 100 mounted coincident with a swing axis 104 of a main frame 110 the receiver supplies the signal to the microprocessor and as an alternative can provide a visual output to the operator of the excavator mounting the depth sensor receiver coincident with the swing axis eliminates the effect of the inclination of the excavator with respect to the horizontal on the liquid depth level device read out device as the excavating machine lowers the end of the stick arm 12 into the trench upon passing through the reference laser plane 32 to the bottom of the trench the depth measuring sensor combined with the inclination of the bucket accurately reflects the depth of the trench again this input is transmitted to the mircoprocessor.