It's a SET button. The icon next to the word is supposed to remind you of a tire. If you change your mind about what tire pressures you want, you can inflate the tires to whatever pressure you prefer, then use the SET button to tell the car "see the pressures in the tires right now? Those are the pressures i want" and it remembers those pressures. Other than that, it doesn't "reset" anything. If you have different tire pressures front and rear, you should use it after tire rotations (well, the tire shop probably already did for you), because the car remembers the pressures by transmitter ID, not by which corne of the car. If you run equal pressures, and you never change your mind about the pressures you want, you'll never have a reason to press it.
