A drilling machine includes a frame, a tower that is supported by the
frame, two tracks for movement over the ground, at least three yokes that
interconnect the frame and the two tracks, at least three hydraulic
cylinders, an inclinometer that senses the inclination of the frame and
produces an output signal that is indicative of the inclination of the
frame, and a controller that receives the output signal from the
inclinometer. The tower includes a drill string. Each yoke is connected
to the frame and one of the tracks. Each hydraulic cylinder is extendible
and retractable in response to an associated control signal and connected
to the frame and an associated yoke. The controller generates control
signals for the hydraulic cylinders such that the hydraulic cylinders are
controlled to extend or retract to maintain the frame in a level
position.