and are time derivatives and are preferably determined as mean values of gradients determined from {HEAD ~ a series} of {TAIL ~ measurement points} 
of
and are time derivatives and are preferably determined as mean values of gradients determined from { HEAD ~ a series } of { TAIL ~ measurement points }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL