Orval Fairbairn writes:

All W & B calculations result from taking the sum of all moments and
dividing by the sum of the associated weights.

Sum (arm*weight) / sum (weight) = CG

The arms are referenced to the datum -- an arbitrary point -- sometimes
the LE of the wing, sometimes a point ahead of the nose; but nonetheless
it is THE reference point for a given aircraft.

The POH will list the arms for each seat, fuel, oil, baggage, etc.

OK, thanks. That doesn't seem too difficult. Apparently "moment" and
"arm" are synonyms (?).

I guess the manufacturer doesn't say exactly what point constitutes
neutral trim.

I've been experimenting with changing the payload in flight (one of
the advantages of a sim) and that helps a bit with figuring out how to
get the most neutral load distribution possible.

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