How does it work?
In principle, it's a restriction plate like NASCAR uses to control horse power and speed. The ET Genie is different in that it is manually "ADJUSTABLE" from wide open, down to less than 20% air flow.
Because it's installed below the carburetor, the throttle is wide full open on every run.  This allows the carburetor circuits to function properly without disturbed air flow patterns caused by the butterfly valves being partially closed, but at the same time reducing the signal (CFM) from the motor.   A nut on either end of the ET Genie is turned  to increase or decrease air flow. This, of course, controls the horse power and your Elapsed Time.
A dial indicator is used to view the restriction amount.