The Department of Agriculture is authorized to test all weighing and measuring devices used in the retail or wholesale sale of liquefied petroleum gas, and shall condemn all such devices which are found (a) to be inaccurate and (b) do not clearly indicate the quantity of liquefied petroleum gas in pounds, or gallons, or cubic feet or other unit approved by the department. It shall be unlawful to use a weighing or measuring device for determining quantities of liquefied petroleum gas which has been condemned by the department. The department shall conspicuously mark all condemned devices, which mark shall not be removed or defaced except upon authorization of the said department or authorized representatives. It shall be unlawful to use a vapor meter dial which is not equipped with a cubic foot indicator for testing the accuracy of the meter.