This value is 1 when {HEAD ~ the cross section} of {TAIL ~ the particle} is a perfect circle 
of
This value is 1 when { HEAD ~ the cross section } of { TAIL ~ the particle } is a perfect circle
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH