I recently bought a new lawn mower. So what has that got to do with design error? I can hear you ask. I looked at the assortment of machines on display and nally settled on two. Choosing between them was difcult. One was a little cheaper; the other had a slightly more powerful engine. Then I imagined myself pushing the mower around the lawn and thought of the ways I interact with it. But of course, the thing I do most often when mowing is empty the grass catcher. I bent down and unhooked the catcher on the rst mower. It lifted away easily. I looked at the way it tted to the machine and noticed the two simple hooks that were designed to sit on a bar above the rear opening. It was immediately clear to me exactly how and where to t it. I replaced it in a second – easy! The human factors issues surrounding person plus machine plus operational environment had been clearly thought through and designed into the device. Full marks to that designer!