I was told that the concave shape holds the product in the center of the pad a little better -- that is, it seems to counteract the tendency of the product to work outward. Something about centrifugal vs. centripetal force? 
__________________ "The perfect finish is a process and not a product." -- Jngrbrdman, 12.30.02
'75 Jaguar XJ6C, red
'93 champagne Mercedes-Benz 190E, '70 VW red Kharmann Ghia
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