{HEAD ~ The velocity} may be measured by {TAIL ~ the use} of light screens, which measure the time required for the ball to travel a fixed distance 
measured by
{ HEAD ~ The velocity } may be measured by { TAIL ~ the use } of light screens , which measure the time required for the ball to travel a fixed distance
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH