A licensed public weighmaster shall not use any scale to weigh a load, the weight of which exceeds the nominal or rated capacity of the scale. When the gross or tare weight of any vehicle or combination of vehicles is to be determined, the weighing shall be performed upon a scale having a platform of sufficient size to accommodate such vehicle or combination of vehicles fully, completely and as one entire unit. If a combination of vehicles must be broken up into separate units in order to be weighed as prescribed, each such separate unit shall be entirely disconnected before weighing and a separate weight certificate shall be issued for each such separate unit.