Except as otherwise provided in any technical regulation or where impracticable, any test load applied to a weighing instrument in the course of a test for errors must consist of measurement standards that comply with the requirements in Part III of these Regulations, provided that where a sufficient number of such measurement standards are not available, suitable constant load, applied in successive quantities not exceeding the total of the available weights, may be used in conjunction therewith to make up the load progressively to or near the capacity of the weighing instrument.