Abstract: A magnetic sensor that measures the angle of the sensor's sensitive axis relative to a local magnetic field compensates the navigation solution of a MEMS-IMU/GPS navigation system. A stable navigation solution is thereby maintained. The magnetic sensor is mounted on a body axis of the vehicle perpendicular the spin axis of the vehicle. As the vehicle spins, the magnetic sensor provides an analog output voltage that varies sinusoidally with vehicle roll with the zero crossings occurring when the sensor's sensitive axis is perpendicular to the local magnetic field. The magnetic sensor measurements combined with knowledge of the local magnetic field relative to the local level reference are used to correct the navigation solution's roll error. Following high rate sampling of accelerometers and gyros, and algorithm to computational de-spin in the navigation solution is executed whereby navigation processing may be implemented with a non-rolled vehicle body frame algorithm.