gauge on left in top picture is the "regulated" pressure from whatever air source you're using and the gauge on right appears to be an "applied" or "test" pressure that displays leakage or pressure difference between the two gauges. The bottom picture has a pressure regulator attached to a t-block and has only one gauge so the gauge really only reads the applied pressure. Looks like the regulator is used as kind of a "bleed off" valve that you manually adjust to bring the test pressure to your desired level by watching the single gauge pressure.
I would rather have the upper gauge/manifold setup with the longer length of hose from the bottom picture, just my two cents. ;)
