A vibrating weighing instrument must as far as is practicable be tested for sensitivity, the ratio of displacement of the indicating element to the increase in the mass of the load which produces such displacement, at any load up to its capacity and at any such load the mass required to effect turn of the beam or steelyard from its position of balance must not exceed the turning allowance prescribed for its class and capacity: Provided further that in the case of the test at capacity the mass required to turn the beam or steelyard from its position of balance excludes the addition of one-half of the applicable turning allowance.