When you first switch on the units they go into automatic 'Align' phase don't they...... .Well, that's exactly what they are doing, aligning with the earths 'North-South' axis i.e.Longitude.. .They also remember in which hemisphere they were shut down.. .All earth accelerations about the 3 axes (x,y,z) are then sensed,and from the relative proportions of each, the heading can be calculated.
This is the 'simple' pilots explanation.If you want the full 'Avionics Engineers' version,just wait, someone will be bound to put finger to keyboard!! <img src="wink.gif" border="0">
[ 25 February 2002: Message edited by: moleslayer ]</p>