{TAIL ~ Plethysmograph apparatus} comprising a measuring cell and a reference cell constructed in {HEAD ~ such manner} that exterior pressure variations cause equal pressure variations in both cells 
{ TAIL ~ Plethysmograph apparatus } comprising a measuring cell and a reference cell constructed in { HEAD ~ such manner } that exterior pressure variations cause equal pressure variations in both cells
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH