In a previous article, Mxsmanic said:
For example, if the average passenger has 10 lbs of carry-on and this
is incorporated into the estimated weight used for that passenger, and
he is suddenly required to check the carry-on, the assumed weight will
be too high by 10 lbs. This, combined with the 10 lbs extra of
measured weight in the luggage in the hold, would make the take-off
weight calculation 10 lbs high. Multiply that by hundreds of
passengers, and you have a weight that could be thousands of pounds
off.

Plus, with all that valuable stuff being checked, the TSA screeners will
steal about 10 pounds worth of stuff per passenger, making the weight
even further off.


--
Paul Tomblin http://xcski.com/blogs/pt/
You cannot run Windows innocently. Guilt of aiding & abetting, at
the very least, is automatic.
-- David P. Murphy