The card machine asked me for a tip before I had my coffee

In my first week I stood at a counter in Wicker Park, tapped my card, and the screen turned to face me with tip buttons. The coffee had not been made yet. Back home I would have tapped away and thought nothing of it. Here, a tip of about 20 percent is simply what people do, and I spent the walk home wondering how an owner sets wages when the customer covers part of them. I did not enjoy the arithmetic, but I understood the screen better after that.