Full atmospheric pressure is close to 15 lb/square inch, so with a pump producing
around 2/3 of a full vacuum the pressure achieved is about 10 lb/square inch.
Remember, the important area is the area of the front face of the vacuum chuck, not the
size of the workpiece. The table shows this area for chucks of different diameters up to
12 inches and the overall force holding the workpiece onto the chuck.