Which test measures indentation depth rather than diameter?

The Rockwell Test is designed to measure the hardness of a material based on the depth of penetration of an indenter under a large load compared to that under a small preload. This method uses different indenters and applies different loads depending on the material being tested. The key feature that distinguishes the Rockwell Test is that it directly measures the depth of the indentation. A dial or digital readout provides a hardness value that corresponds to this depth measurement, allowing for quick and efficient assessment of material hardness without requiring complex calculations or additional steps.

In contrast, the other tests mentioned involve measuring the size of the indentation in terms of diameter or other dimensions, which is not the case for the Rockwell Test. The Brinell and Vickers tests require measuring the diameter of the indentation left in the material, while the Knoop test measures the long diagonal of the indentation. This characteristic of directly measuring indentation depth makes the Rockwell Test particularly advantageous for certain applications, as it simplifies the hardness testing process.