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