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