you have to lift it more then once b/c its best just to double check because when adjusting the front the back can go out and you may have to readjust.
That's my point! You could get 25 different readings from that deal.
I know when I worked in a race shop setting up real race cars, I would spend plenty of time just getting my scales 100% accurate as far as level and on plane with each other, before ever setting the car on them.
I cannot imagine loading and unloading the car 10 times, inadvertantly, one or more of the scales would be moved, altered or otherwise disturbed, thus causing an error in measurement.
Just a thought. I think I'll use the old postal scale method and a calulator. Simple math and you can calculate crossweight (wedge) and percentages.