Durometers measure the elasticity of materials such as natural rubber, neoprene, polyesters, leather, nitrile, and vinyl. The measurement is based on the degree of the material’s resistance to permanent indentation. Shore A durometers can measure more flexible materials, such as the rubbers used to make hydraulic O rings and automotive tire treads. Shore D durometers can measure harder materials, such as those used to make hard hats and solid truck tires. Analog durometers have peak retaining hand functions that help provide error-free readings. Digital durometers have a data hold function that can retain readings on the LCD or allow them to be downloaded to a computer.