A non-contacting range sensing and control device for controlling the position of a grading implement relative to a datum is disclosed. The device includes a non-contacting distance measuring device that periodically measures the separation distance between the distance measuring device and the datum. Also included is a reference circuit that defines consecutive first, second, and third intervals for comparison to the separation distance, and a comparison circuit that periodically compares the intervals to the separation distance, and generates a positive error signal if the separation distance is within the limits of the first interval, generates no error signal if the separation distance is within the limits of the second interval, and generates a negative error signal if the separation distance is within the limits of the third interval.