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