The q switch(es) is(are) measuring airspeed. It depends on the airplane line no.
The later -200 a/c had 2 or 3 q switches 1st s/w activated at 25 units repositions to 20 and back to 25 with reducing a/spd. With flap lever at 30 2n/d s/w is activated and the flaps are driven to 25 units or 20 units depending on a/spd., reducing spd repositions flaps back to 25 or 30 units.
The actual a/spds I'd have to go look up!