Product Usage: 1. Place the Spark Plug into tester hole 1 or 2; If you want to compare the new spark plug and old one, place new spark plug into hole 1 and the old on into hole 2. 2. Connect to power supply. 3. Turn the key switch 4 clockwise to turn on tester, indicator 3 will light up, tester is now working at 1000rpm/min. 4. Again turn the key switch 4 clockwise,you can adjust the working frequency between 1000rpm to 6000rpm/min. The higher the frequency, the stronger the spark strength. Specification: Mold: spark plug tester Input: 100~240V AC Length of external: 1m Host size: 145*90*114mm power supply: Power Adapter Power Adapter: Output 12V 1A DC Suitable for 12V driven gasoline car spark plugs Usage: Test car spark plug performance and ig.