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