{HEAD ~ The pressure sensor} comprises {TAIL ~ either a door}, whose movement is measured without contact, or a sensor, whose movement is measured optically 
{ HEAD ~ The pressure sensor } comprises { TAIL ~ either a door } , whose movement is measured without contact , or a sensor , whose movement is measured optically
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH