The Rockwell hardness test is usually thought of as a method that measures the hardness of a material. A more accurate description might be that the Rockwell hardness test only provides an estimate of the absolute “true" hardness value. It is only an estimate since, like essentially all measurement systems; there is always some level of error in a Rockwell hardness measurement. For a hardness measurement to be useful, the level of error must be small enough to meet the user’s needs.
The total error in a measurement is often the result of a combination of errors from multiple sources. In the case of a Rockwell hardness machine, errors associated with machine components, testing cycle variations, and environmental conditions, as well as other sources, contribute in varying degrees to the overall measurement error. When it is practical, the measurement result should be corrected for these errors. However, in many cases, the errors may occur randomly and cannot be corrected. In other cases, the errors may be systematic, but there may be valid reasons for not correcting these errors. Even when corrections are made to compensate for the errors, there will be an additional error associated with the correction. These uncorrected errors then account for an “uncertainty" in the accuracy of the measurement result. To have confidence that the result of a hardness measurement is appropriate for a particular application, some understanding of the level of uncertainty in the measurement must be known.