Views:

The PG7607 piston gauge is a special application piston gauge system for low pressures from 5 kPa to 25 kPa.  It uses a controlled clearance piston-cylinder.  The piston-cylinder and platform are not interchangeable with the PG7601 piston gauge.

http://us.flukecal.com/literature/product-manuals/pg7000%E2%84%A2-piston-gauges-operation-and-maintenance-manual