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to be standardized on a master scale of the capacity of the car. Also since the wheels, brake shoes, air brake connections, etc., are part of the standard weight such a car must be constantly checked on the master scale. This equipment is satisfactory for a railroad where the hauls from the master scale to the scales to be tested is not great, or where the operations are restricted to a single state, but plainly such an equipment would not answer the purpose of the bureau since it expects to send the car to all parts of the country, and it would not be possible to establish the necessary master scales at enough points to insure the correctness of the test ear. The car of the bureau was therefore designed to reduce the wear on the equipment to a minimum, and this is accomplished by carrying a specially built, short, six wheeled truck, and 100,000 pounds of standard weights inside a box car which is equipped with the necessary power to operate a crane for handling the truck and test weights. The test weights consist of eight 10,000 -pound, four 2.500-pound weights and ten thousand pounds of 50-pound weights. The total error of the eight 10,000-and the four 2,500-pound weights, is less than half a pound and since the large weights are bolted down to the floor of the car in shipment from one scale to another and are very carefully handled when used, there is no reason why they should change appreciably in a year. The same is practically true of the truck, which may, in a test of a 52-ft. scale with three different loads, travel about 300 feet or about sixty miles in testing 1,000 scales. As this travel would be at a very low speed, and without the application of brakes or the accumulation of dust or mud, it is hardly conceivable that its weight will change as much as five pounds in a year, an amount that would be insignificant in the combined weight of the truck and test weights. The truck which is operated by an electric motor supplied with current from a gasoline engine generator in the box car weighs 5,059 pounds.

Fig. 1 shows the general arrangement