I was under the impression they had to be calibrated
on a regular basis anyway? With the records kept.
Or maybe not...
Airlines investigated over baggage check-in failures -Times Online
As an aside, I did the same thing in Cancun a few weeks
ago, there the weight could vary by a few kilos dependant
on how central to the scales the bag was, however, the
system there uses one set of scales for two desks so
the surface area is much larger.
Regards
DaveA