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Specifications of a method for the determination of the indentation hardness of plastics by means of the Rockwell hardness tester using the Rockwell M, L and R hardness scales. The Rockwell hardness number is derived from the net increase in depth of impression as the load on an indentor is increased from a fixed minor load to a major load and then returned to the same minor load. For materials having high creep and recovery, the time-factors involved in application of the major and minor loads have a considerable effect on the results of the measurements.