See this instruction sheet for what's included (fittings and interconnect tubing) with a DVU. The enclosure is the same as that for a PPC4 pressure controller so the rack mount kit for a PPC4 can be used to rack mount the DVU in a standard electronics rack.
See this Application Note for information on when use of a DVU is beneficial,
Low Pressure (Draft Range) gauge & negative gauge calibrations
Below image is of a PPC4 Pressure Controller with a DVU on top of it. Vacuum pump and pressure gauge are also shown.
Contact Pressure Technical Support at the below link or by calling +1-877-355-3225 for more information or questions.