Calibration of a machine used in the Bureau of Mines during World War I to test the hardness of steel for military purposes. The Brinell hardness test involved applying known pressure with a hard steel ball and measuring the depth of the resulting impression. A device was used to weigh the hydraulic pressure and ensure its accuracy. Date: November 14, 1918.

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Photo credit: © piemags/NSC / Alamy / Afripics
License: Licensed
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Keywords: activities, american, ball, brinell, bureau, calibration, correctness, depth, device, hardness, hydraulic, impression, instrument, machine, measurement, metal, military, mines, pressure, steel, test, testing, war, work, world