The apparatus 15 wherein said calculating means comprises operational amplifiers configured in such a way as to calculate {TAIL ~ said first voltage} and {HEAD ~ said corrected current} 
The apparatus 15 wherein said calculating means comprises operational amplifiers configured in such a way as to calculate { TAIL ~ said first voltage } and { HEAD ~ said corrected current }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD