The invention is based on the recognition that an extremely rigid construction of {HEAD ~ the measuring cell} is not necessary, provided that the compensation of the exterior pressure variations is carried out with {TAIL ~ sufficient accuracy} 
The invention is based on the recognition that an extremely rigid construction of { HEAD ~ the measuring cell } is not necessary , provided that the compensation of the exterior pressure variations is carried out with { TAIL ~ sufficient accuracy }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL