In order to assess the specimen’s hardness, a test bar with a known BHN value is chosen. The test bar’s BHN must be within 15% of the specimen’s BHN and be made of the same basic material in order to maintain consistent accuracy. (Using carbon steel bars to test non-ferrous materials leads to impact errors that need to be corrected for when the test results are applied.) The test bar is put into the Telebrineller apparatus, which is then set upon the specimen.

The instrument’s bar is taken off, and the Telebrineller Microscope is placed over the necessary impression. The scale provided by the microscope has divisions of 1/10 millimetres, and it is made to be bright and visible to the observer. The diameter is determined by the division that lies over the opposing tangent and is oriented tangent to the impression. Within.05 millimetres, readings can be done with ease and accuracy. In the same way, the impression in the test metal is measured. It doesn’t take long for either measurement.

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