Sentence:  When values of temperature derived with this instrument were compared with the accepted values associated with liquid helium 4 <WSD>vapor</WSD> pressures , differences of about 10 and 7 millidegrees respectively were found . 
Meaning of the word marked with <WSD> tags:  the pressure exerted by a vapor; often understood to mean saturated vapor pressure (the vapor pressure of a vapor in contact with its liquid form)