another image of the checkout counter at a deli in Rockville, Maryland. We saw before the pattern of customers standing and awaiting completion of their purchases, and wearing away the floor tiles with their shuffling feet, revealing contours of their use.
Her we see the wear patten made by their purchases that are placed and slid across the counter to be totaled up on the register. The white of the counter top has been worn away to the brown board underneath. There is greater wear near the customer who perhaps sets down several items, but the wear patten narrows as the checker selects one at a time to ring up their prices on the register. What remains is the pattern of support for the joint distribution of purchase placement.
But there's more (as they say on TV commercials). Look along the front edge of the counter nearest the customer. Along this edge we see the bell-shaped marginal distribution of left/right item wear as the items are either placed on or slide off the counter.