Sentence:  Rockwell hardness test: A method of measuring hardness. The hardness is expressed as a number related to the depth of the residual penetration. A test for determining the hardness of a material based on the depth of penetration of a specified penetrator in to the specimen under certain arbitrarily fixed condition of test. A hardness test where the loss in kinetic energy of a falling diamond tipped metal ‘<WSD>tup</WSD>', absorbed by indentation upon impact of the tup on the metal being tested is indicated by the height of rebound. 
Meaning of the word marked with <WSD> tags:  The head of a hammer, and particularly of a steam-driven hammer.