Application Range: 12V Gasoline vehicles car spark plugs Car Spark Plug Test principle: Car Spark Plug Tester User Manual: 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 5000rpm/min. The higher the frequency, the stronger the spark strength. Gasoline Car Spark Plug Tester Product Parameters: Main Unit Size:145*85*60mm Main Unit Weight:220G( Not including Power Adapter) Power Adapter: Input 100-240V AC / Output 12V 1A DC.