Usage: Open the battery box, put into 2 * AA battery and close the box. Press the POWER button, there will display 9 seconds count down. Then the display will flash "C", and right now you can breathe out 3 seconds evenly to the air intake. After one beep sound, it will display the result, the result will display 5 seconds, and shut off automatically. If you want to test one more time, just press the Power button again.
5 levels result: Verygood, normal, not sogood, bad, very bad.