Brief description:
One way to describe how it works is to think of 3 beer bottles. One empty, one 1/2 full and one 3/4 full. If you blow across the top of each bottle they will produce a tone from low to high in pitch. The empty bottle having the lowest pitch.
The pitch of the tone represents the volume of air in each bottle.
Less brief:
First Hook a supply of compressed air to the whistler. Then with the calibration bottle hooked to the whistler adjust the flow meter. Calibrate the whistler with a calibration bottle to account for weather/air density. Then choose the correct spark plug hole adapter and insert the the whistler onto the cylinder. The whistler has 2 tubes hooked to it. One to blow air into the whistle and one to listen for the pitch. Next turn the crank to place the piston at TDC. Now enter the cubic inch displacement of the engine and the number of cylinders. The machine now knows the volume at TDC from the pitch and the volume at BDC from the cubic inch and number of cylinders entered and then can then calculate the compression ratio.
