What is the basic principle of a digital Vickers hardness tester?

Taiwan Nakazawa Co., Ltd. answers for you: The basic principle of the digital Vickers hardness tester test is that the indenter uses a 136° angle pyramidal diamond indenter.
The loads for Vickers micro-hardness testing are: 1 kg, 2 kg, 3 kg, 5 kg, 10 kg, 20 kg, 30 kg, 50 kg, and 100 kg. Commonly used loads are 1 kg, 2 kg, 5 kg, 10 kg, 30 kg, and 50 kg. The required thickness of the specimen depends on the magnitude of the load.
The hardness indentation test is expressed by the load per unit area. A fixed selected test force (load) is applied to the surface of the sample, followed by a predetermined holding time (dwell) and the removal of the test force (unloading). A residual indentation remains on the surface of the sample in the shape of a square pyramid base. By measuring the length of its diagonals with a micrometer eyepiece, the diagonal length of the indentation is obtained. The hardness value is calculated by the ratio of the test force to the surface area of the indentation.