Sentence:  The reproducibilities of helium <WSD>vapor-pressure</WSD> thermometers have been investigated in conjunction with a `` constant temperature '' liquid helium bath from 4.2 to 1.8 * * f . 
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)