The slope angle of a blade on an earthmoving machine is automatically controlled based on measurements from a three-axis gyroscope, a blade slope angle tilt sensor, and a blade tip angle tilt sensor mounted on the blade. A three-axis gyroscope has high dynamic response and high resistance to mechanical disturbances but is subject to potentially unbounded errors. A tilt sensor has bounded errors but has a slow dynamic response and a high sensitivity to mechanical disturbances. The combination of a three-axis gyroscope and two tilt sensors provides an advantageous measurement system. Algorithms for performing proper fusion of the measurements account for the lack of synchronization between the three-axis gyroscope and the tilt sensors and also screen out invalid measurements from the tilt sensors. The blade slope angle is controlled based on a reference blade slope angle and an estimate of the blade slope angle computed from properly fused measurements.