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