The commission may test or calibrate weighing and measuring devices used in the retail sale of liquefied petroleum gas, either in liquid or vapor form, and shall condemn all devices found not to be within the permitted tolerance or which do not clearly state the quantity of liquefied petroleum gas, either in liquid or vapor form, in pounds, gallons, cubic feet, or other units approved by the commission. The commission shall conspicuously mark all condemned devices, which mark may not be removed or defaced except upon authorization of the commission.