CHARLOTTE, N.C. — An NBC Charlotte investigation uncovered that about one in 20 gas pumps in North Carolina are giving you the wrong amount of gas. 

The Defenders dug into this story -- tagging along with state inspectors as they try to find and fix those faulty pumps.

State inspectors test every gas pump at least once a year to make sure you're not getting cheated.

Randy Ramsey is one of the guys who's making sure you're are getting exactly what you pay for.

"I want to make sure we don't have any run-up or computer jump as we call it."

State standards inspectors like Ramsey pump exactly five gallons from every pump and see how spot on the price is.

"That pump it was minus one square inch."

That means it was about a half ounce off.

"I record the error."

The acceptable range is plus or minus six square inches, or three ounces, in the five-gallon test.

The North Carolina Department of Agriculture said 4.9% of pumps failed the calibration test last year. That's about one in every 20 pumps statewide.

But that doesn't necessarily mean you're getting ripped off. 

"A lot of times we find it's actually in a customer's favor; they're getting more product than they're paying for."

In cases when the pumps are overcharging you, don't assume it's a calculated rip-off. 

"Have there been cases of the store being at fault and doing it intentionally?" asked NBC Charlotte's Savannah Levins.

"I have not personally found one that I thought it was intentional. most of the time it's a defect in the equipment."

Here's what to do if you want your pump to be right on the money.

"Look on your pump and see if it has a current approval seal on it, it will tell you when the dispenser was inspected." 

If you find an issue, gas pump protectors like Ramsey, are just a call away. 

If you do ever feel like somethings not right, you can call the number on the sticker that's usually on the pump. You can also file a complaint online.

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