earliest work was finished by Bulychev, Alekhin, Shorshorov in the 1970s, who determined that Young's modulus of a material can be determined from the slope of a force vs. displacement indentation curve as: : material stiffness, which is the slope of the curve : the tip-sample contact area : reduced modulus, defined as: Where and are the Young's modulus and Poisson's ratio of the sample, an and are that of the indenter. Since typically, , the second term can typically be ignored. The most critical information, hardness, can be calculated by: Commonly used indentation techniques, as well as detailed calculation of each different method, are discussed as follows. Macroindentation tests The term "macroindentation" is applied to tests with a larger test load, such as 1 kgf or more. There are various macroindentation tests, including: Vickers hardness test (HV), which has one of the widest scales. Widely used to test hardness of all kinds of metal materials (steel, nonferrous metals, tinsel, cemented carbide, sheet metal, etc.); surface layer / coating (Carburization, nitriding, decarburization layer, surface hardening layer, galvanized coating, etc.). Brinell hardness test (HB) BHN and HBW are widely used Knoop hardness test (HK), for measurement over small areas, widely used to test glass or ceramic material. Janka hardness test, for wood Meyer hardness test Rockwell hardness test (HR), principally used in the USA. HRA, HRB and HRC scales are most widely used. Shore hardness test, for polymers, widely used in the rubber industry. Barcol hardness test, for composite materials. There is, in general, no simple relationship between the results of different hardness tests. Though there are practical conversion tables for hard steels, for example, some materials show qualitatively different behaviors under the various measurement methods. The Vickers and Brinell hardness scales correlate well over a wide range, however, with Brinell only producing overestimated values at high loads. Indentation procedures can, however, be used to extract genuine stress-strain relationships. Certain criteria need to be met if reliable results are to be obtained. These include the need to deform a relatively large volume, and hence to use large loads. The methodologies involved are often grouped under the term Indentation plastometry, which is described in a separate article. Microindentation tests The term "microhardness" has been widely employed in the literature to describe the hardness testing of materials with low applied loads. A more precise term is "microindentation hardness testing." In microindentation hardness testing,