Shore hardness is measured on a device called a durometer. Durometers use specific, standardized methods for measuring the hardness of plastics and elastomers. Durometer numbers represent a relative comparison of the hardness between different but similar materials that have already been measured using the same durometer device, scale, and measurement standard.
To perform a Shore hardness test, a durometer gauge featuring a spring-loaded steel rod will compress the surface of a material and provide a reading of the resulting indentation. Performing a Shore hardness test involves three basic steps: