That's right. When you use the chronograph to time an object moving over a measured distance the Tachometer scale displays the speed.
With regards to the frequency of 21,600 v/h (3Hz) this really isn't relevant to the seconds hand. The flying seconds hand actually "jumps around the dial 16 times a second" and "are driven by both the going train of the movement, working off the barrell, and the chronograph train, working off the barrel arbor."
I really liked the feel of the rocker. It was complete natural feeling and very easy to use. Great concept!