From Texas Standard:
The morning routine of Kai Alterman includes a stop at a café and a cab ride. When it comes time for her to pay, the server slides her credit card, then hands her a screen similar to an iPad to sign – complete with choices of how much to tip. Alterman hits the middle option, leaving a 20 percent tip.
"I think this makes people tip more often, because you feel more guilty not to tip with those," Alterman says.