CIMU Calibration Background
The Mk III Transceiver contains an IMU (called the "Cerulean IMU") that has internal magnetometers, accelerometers and gyros. These sensors are imperfect and can have manufacturing bias and linearity errors. Additionally, external magnetic disturbances can cause the magnetometers to make a bad estimate of magnetic north. Calibration mitigates the effect of these factors.
The gyros and accelerometers are subject to slight aging effects, and to temperature effects. Generally, you really only need to calibrate these every three to six months.
The magnetometers are subject to variations in the Earth's magnetic field strength and to magnetic disturbances due to electrical currents and and nearby soft iron or other ferrous objects. The closer a disturbance source, the smaller it can be and still affect north-finding. Generally, you should calibrate the magnetometers when you move the system a geographically significant distance (e.g., 50 km or more), or to an magnetically different location.
See the following sections on CIMU calibration procedures.
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