When test units with a large internal volumes should be calibrated with it (e.g. pressure gauge from NS 100). For pressure transmitters with a small channel bore volume, a shut-off valve is needed. The volume change of the piston with a complete spindle hub is only 3.9 ccm In addition, a check valve is necessary when reference devices are used with large internal volumes (e.g. NS100 pressure gauge). When using the CPH series reference pressure transmitters and pressure transmitters on the test item side, a shut-off valve is required.