The ASTM D 2240-15 (2021) is a standard test method for determining rubber Hardness for twelve different types of hardness gauges, such as A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and Type R. The method evaluates a material's Hardness characteristics by measuring its indentation Hardness formed under specific conditions, which correlates with the material's resilience modulus and viscoelasticity behavior. However, different types of hardness gauges and measuring instruments can lead to different measurement results, so there is no simple correspondence between different instruments. This test method does not apply to coated fabrics, and it is recommended that the Miscellaneous hardness testing method be considered when using Miscellaneous materials other than certain types of materials. All measurements of the mass, force, or dimensions of the material, instrument, or equipment shall comply with the requirements of the National Institute of Standards and Technology or Miscellaneous's internationally recognized organization to ensure traceability and accuracy of results.