NATHAN HUNSINGER / DMN

An overweight suitcase could cost you.

Thanksgiving is just about a week away and the chances are many of you will packing up and flying out to visit family.

But consider this: when you check a bag at the airport, the baggage scale may be wrong.

What's in a number?

At the airport, a bag over 50 pounds can mean a $50 fee.

"We never check, but we trust," said David Ball, a traveler.

So, how accurate are those baggage scales?

Ball, an avid American Airlines traveler, wants to know.

He worries he's paid the price for bags that were never overweight.

"If I know my bags are well within the limits and they say that they're not, I'll be very angry," he said.

2006 state inspection records show the two biggest airline carriers in North Texas are off: Southwest and American Airlines.

Numbers show at Southwest's Love Field operation, out of 10 scales, 4 were off.

As for American, of their 200 scales, at least 13 weren't right.

One at D/FW was 10 pounds overweight while another at Love Field was 14 pounds over.

Tim Smith with American says numbers like that are unheard of.

"We would have shut those scales off immediately because they're not within anyone's tolerances," he said.

"To hear that they're off 10 pounds or more that's extraordinary. That's down right criminal," said Ball.

The state requires all airlines to calibrate scales once a year but it only inspects them every four years.

And before the inspection, the airlines get a 24 hour heads up.

Yet after a round of testing at both airports, nearly 40 scales were still flat out wrong.

Steve Gilpin, is a weight expert, and sells scales to the airlines.

"You'll probably find that when scales are off, they probably weigh light more than they do heavy," he said.

North Texas Scales says if dirt or trash gets underneath the scale, it measures in the consumer's favor.

And we did find a lot of that.

One scale was 7.6 pounds under at D/FW's American Airlines.

Another was 14 pounds under at Southwest Love Field.

And while Southwest only calibrates scales once a year, and calls its record good for the customer, American devotes an entire team of mechanics to the cause every day.

"As soon as they get to one end, they go back and start at the other," Smith said.

But American doesn't have control of every scale.

D/FW airport runs terminals D and E and despite efforts to be quote "as accurate as possible," some scales were off, including one which was 14.2 pounds under.

We wanted to test it out for ourselves, so I packed a bag and it tests out right at 23 pounds.

How do we know that's right?

We needed to calibrate the scale first.

"In order to calibrate a scale, you need a known test weight," said Gilpin.

Like a 50 pound weight.

If the scale doesn't read 50, the computer inside is reprogrammed.

With our bag ready -- we set out how hard it would be to find an inaccurate scale.

The first scale was right on the money at 23 pounds. The bag then came in twice as under by a pound. On the fourth scale, it came in as overweight at 24.5 pounds.

And from Ball's experience, whether it's one pound over or 10, it will cost you.

"It looks kind of like a money grab," Ball said.

American Airlines it does not make money by charging for overweight bags.

In fact, American says if each aircraft in the fleet added 100 pounds of unnecessary weight, it would cost the airline $3 million a year.

This is the reason they pass the bill on to you.

"If it says 50 pounds, it should be 50 pounds," said Ball, so you don't pay $50.