Figure 2:  Idealized, cutaway section through a TILT-OBS; expanded view illustrates the high sensitivity tiltmeter.  Two orthogonally mounted low gain inclinometers are mounted on the center ring, and the high gain inclinometers and the high sensitivity tiltmeter are fixed to the seismometer block.  The tiltmeter is mounted on a triangular plate that is  independently leveled with motor-driven micrometers.  The dynamic range of the high gain  inclinometers is matched to the tolerance of the OBS leveling mechanism.