Sentence:  This , however , can only be considered approximate , as the diameter of the <WSD>pulley</WSD> was increased by the build-up of tape and the tape was occasionally removed from the pulley during the runs . 
Meaning of the word marked with <WSD> tags:  a simple machine consisting of a wheel with a groove in which a rope can run to change the direction or point of application of a force applied to the rope