On Monday, November 9, I filled up my empty gas tank at a station in Mira Mesa. (The tank was so empty, the car had stalled once just before I reached to the station.) After I’d filled up, the gauge on the pump indicated that I’d dispensed 12.266 gallons. My car’s manual shows the tank holds only 11.9 gallons.

I reported the discrepancy to the cashier, who at first ignored me. After repeating myself two more times, he just shrugged his shoulders. At that moment I felt that the station was ripping me off and wondered how many others were paying for gas they weren’t getting.

When I arrived at home, I immediately logged on to the California Weights and Measures website in order to lodge a complaint. The procedure is to download a form and mail it, which I did.

On Thursday, November 12, I received a phone call from a representative of the agency. He confirmed details and said an inspector would get in touch with me. To my surprise, an inspector called me the next day to say that an investigation had been completed.

Standard procedure is for the inspector to take a five-gallon container to the station, fill it, and compare the gauge to the amount pumped into their calibrated container. The pump passed that test.

Next, the investigator inspected the tag that was placed on the pump at its last inspection, which happened to be in 2007. The seals on the tag had not been tampered with. How could this be? The inspector explained that vehicle manufacturers estimate the fuel capacity of gas tanks, and the difference between actual and stated volume can be up to 20 percent.