A container used to determine the accuracy of a meter.
To check a pump meter, an inspector would dispense product from the pump into the proving can. When the pump meter shows that the amount dispensed is 5 gallons, the operator then checks the liquid level in the container to verify that the amount there is, indeed, 5 gallons. Minor variances are permitted and the normal allowed variance is plus or minus 6 cubic inches per 5 gallons of product. This is a variance of 0.5 percent.
If the pump meter records a significant inaccuracy, the pump can be officially removed from service until it is adjusted to accurate condition. Calibration of larger meters, such as those used at loading racks, is obtained through use of prover tanks.
See also Prover tank.