Counter Top Wear

Pattern of wear on a counter top at a used bookstore. The brown plywood is the vertical back side of the counter (the checker's side). The blue laminate top has been worn away by book purchases that are set and slid across the counter as price stickers are read and the purchase is rung up. A bell-shaped pattern of wear is centered on the middle of the counter top spreading its two tails along this back edge where the checker rings up the purchase.

See bivariate wear on a counter top here.