Only used by "Go To Stage". A whole number from 0 to 9 — 0 is off, 1 is
the first stage. How many stages a vehicle actually has is decided by whoever
built it; most run 1 to 3. A "Cycle Stages" key shows the live count on its
status line, so you can read the real ceiling off it while you sit in the car.
A stage the vehicle does not have simply does nothing.