Mutt,
Every time the manufacturer nominates a useless datum for W&B calculations (ie most of the light aircraft POHs following the ICAO/GAMA guidance procedures), the datum and everything else gets reworked to improved trimsheet accuracy... this is the reason most of the large aircraft have a nice datum for the hangar guys and an even nicer (but quite different) trim datum for the trimsheet designer .... it does confuse the pilot sometimes which is why I adopt a bit of a hobby horse attitude to this sort of topic.
The other main consideration (an everytime thing) is to consider design assumptions and simplifications, as well as crew and pax etc. movement in flight. The usual way to address this is to do the sums and fudge the envelope limits to negate the effect of the errors. LMCs are in the same general category.
Last edited by john_tullamarine; 12th May 2002 at 14:05.