Recently we built and launched A Good Enough Guestbook, a place where you can send us doodles and they’ll print out on our little printer. It’s quite lovely and fun, and you should send us a doodle. We might also have more in store for these printers in the future. In the meantime, it took a bit of finagling to get the doodle interface feeling just right. One issue we ran into was that users would sometimes tap “Undo” a whole bunch in rapid succession. This undo’d just fine, but on ...