If the sensor should move from its intended horizontal position due to roll, pitch or slamming in a seaway, the sensor will pick up some of the vertical field, mixing it with the horizontal field and causing an error in actual course. It is a seldom recognized fact that this extra isolation from vessel motion, coupled with fluid damping, results in a conventional fluid compass having much greater stability than any electronic compass under most conditions. At mid latitudes in the U.S., one degree of sensor tilt off horizontal will have an apparent two-degree shift in indicated heading, even though the vessel is still on course. In higher latitudes where the horizontal field decreases in strength and the vertical field increases, one degree of tilt can cause over 10 degrees compass error. A few electronic compass manufacturers fill their compass sensor with a heavy oil to dampen the gimbal action and minimize these vertical field errors.
Some designs use more sophisticated signal processing, but the end result is roughly the same.
Any delay in autopilot response to heading changes, especially in quartering seas, results in excessive yaw and the need for excessive rudder corrections. Some electronic compass manufacturers recognize this deficiency by offering a rate gyro which provides a more current short-term heading reference than their sluggish and over damped electronic compass is capable of. They recommend that this button be activated when a change of course is made. This button simply changes the compass damping to minimum and is a tacit admission that the normal amount of damping, which is required to provide a steady display, causes such a delay in heading indication that the helmsman would overshoot a course change. Clearly, any autopilot using this heading information would have great difficulty steering in quartering seas where immediate correction of course changes is essential.