Any basic 2d machine control will do slope off a laser. You need a laser that will slope but it must be in a straight line or you will need to move it every time the angle moves. 3d machine control uses a total station with control points. You either make them or a surveyor sets them for you. It typically works off a prism on only one side of the blade using slope, and rotation sensors to control the rest of the blade. Lasers are more accurate and run off of 2 sensors one on each side of the blade. A machine control panel activates a custom made valve that attempts to keep the sensors on the beam.