Here is a joint distribution of wear on the counter top of a Home Depot. The counter top was originally white. This has worn away to reveal various layers of shading in the laminate and further into the underlying wood of the table. The innermost area has been actually gouged out by many tools, cans of paint, and other heavy hardware. We see nested triangular patterns of wear revealing the joint distribution of tool placement on the counter and their movement across the checkout scanner.
But wait. There's more, as they say on infomercials. Not only do we get the joint distribution of wear, we also get one marginal distribution of wear along the front edge of the counter. As customers drag their purchases onto or off of the counter they leave a bell-shaped pattern of use along that front edge.
