The local cat scale (near the Port of Oakland) charges based on whether it's certified or not. The certified weights are for the State scales.. if they disagree, and the trucker gets a ticket because he belived he was under-weight from the Cat scale, they pay for the ticket.
There is also 3 pads, not 2. One for the front axle, one for the rear axle, and a 3rd pad for trailer. Just make sure your front axle is on the frond pad, the rear axle on the middle pad, and the trailer (if there is one) on the rear pad.
The form they will give you looks like this: