When I am dead, I hope it is said;

The GPS actually gives you a keypad on the TFT screen, but it greys out the letters that don't appear next in any of the entries in its dictionary. A handheld GPS, I imagine, would use the nav arrows as you suggest. (Mine's mounted in my car.)

Dr. Hawking's synthesizer, as I recall, has three inputs: up, down, select. It's been twenty years (or a little less) since I've seen him speak, though.