99% certain the positioner is (sorry, can’t remember proper name for the type of switch, but) on/off, so you step on the switch to turn it on and it runs at your set speed, then you step on it again to turn it off…
EDIT: actually, the manual doesn’t appear to say.
And, at least in the case of the “Make It Extreme” gang
when they built their own, they made it momentary on and reverse switches, so, now I’m more like 50% sure it might be as I described above, and 50% sure it might be momentary, making me 100% sure I have no idea…