A liquid proving system is provided with a small volume liquid prover draining into a liquid holding tank that has capacity for multiple proving measurements. The small volume liquid prover is top-filled and bottom-drained. A liquid holding tank baffle assembly contains saturated vapor from an initial number of fills of the liquid holding tank within the small volume prover to improve overall accuracy of the proving measurements. When liquid is pumped into the prover evaporation of the liquid being pumped into the prover, and release of vapors from the prover and into the entire holding tank, is inhibited due to the saturated vapor environment established by a saturated vapor volume in the prover, which results in a more accurate prover measurement of liquid pumped into the prover. The saturated vapor volume is contained with a vapor tank baffle assembly in the liquid holding tank; a vapor conduit connecting the interior of the liquid holding tank to the interior of the prover; and the interior volume of the prover.