the pressure to obtain equilibrium using the pvs module connected to port 15 in all modes of operation where port 16 is used to establish zero tare the most precise pressure is obtained when the pressure applied to port 16 is regulated using a second piston pressure gage in the high range gage mode one pvs module 100 is connected to port 16 while ports 15 and 25 are open to ambient atmosphere in a preferred embodiment the approximate pressure range in this configuration is 10 to 2500 psi due to the relative ease of switching to the low range mode for making measurements with zero tare no zero tare mode is needed for high range operation the next section of table i shows the necessary connections for high range low range and zero tare low range operation in the absolute mode in the absolute mode a highly stable vacuum approximately 10 mtorr is applied to port 25 using one pvs module 100 another pvs module 100 is connected to port 15 for low range operation or to port 16 for high range operation in the low range configuration a highly stable positive pressure can be applied using a third pvs module 100 connected to port 16 to operate in the zero tare low range absolute mode pressure ranges in the absolute mode are essentially the same as for gage mode configurations there are two configurations for negative gage pressure operation with one pvs module 100 connected to port 25 negative gage mode with a pressure range of minus 0 25 psi tare pressure.