To calibrate a hardness tester, the Morehouse Brinell Calibrator is simply inserted into the tester in place of the usual metal specimen. The load is applied to the Brinell Calibrator and the resulting deflection is read on the indicator. The error of the hardness tester load is determined by dividing the deflection of the Brinell Calibrator under load into the difference between the actual deflection and what the deflection should be for the load being calibrated.