While the slide is in {HEAD ~ motion}, rolling friction characteristics are measured by {TAIL ~ a force gauge} 
While the slide is in { HEAD ~ motion } , rolling friction characteristics are measured by { TAIL ~ a force gauge }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL