Gaging Tools and Methods: Measuring Instruments Used by Machinists and Toolmakers. E-book. Formato PDF - 9780243780013

The standard bar thus marked was taken to Washington and com pared with the government standard Bronze No. 11 and also with Low Moor iron No. 57. In comparing these standards, a method was employed very similar to that used in marking. The bar, properly supported, Was placed upon a box that rested upon rolls and onthis same box was placed the government standard with which the Brown Sharpe standard was to be compared. Both the government standard and the bar to be tested were placed in position under the microscope and by the micrometer screw of the microscope the variation between the two was measured. Three comparisons or tests were made on each end before determining the reading of the microscope, and after these comparisons the value of the B. S. Standard No. 2 was found to be inches for the yard, and meter for the meter. After completing this work, a second standard known as No. 3 was prepared, and comparison with the government standard showed the error to be inch for the yard, and 0000005 meter for the meter. After establishing a yard in this manner, the next problem was that of obtaining an inch; this was done by subdividing the yard into two equal parts, and then further subdividing these two divisions into three, and the three into six, thus giving thirty-six subdivisions or inches.