A set of magnetic measurements can be taken at 110, 55, 27.5, or 13.75 Hz rate.
Tilt sensor is driven with a constant 55 Hz pulse.
Compass heading is calculated 13.75 times per second from the 5 filtered measurements.

The pitch and roll ranges are limited to 40 deg. This will be sufficient for us for the time being.
The attitude info will be extended by solid state gyro's.

dip tilt must be explained !! TO DO !!