An orientation tracking system including a first tracking system subject to drift. A second tracking system is configured to provide an output for calibrating the first tracking system to reduce the drift of the first tracking system. The second tracking system includes at least one inclinometer, each inclinometer including a light source adjacent one side of the inclinometer, a light sensor adjacent an opposing side of the inclinometer, and a light obscuring material within the inclinometer for obscuring the light between the light source and light sensor to indicate an orientation of the inclinometer.
