ANCEL SP02 Car Spark Plug Tester with Auto Adjustable Double Hole Detector Ignition Plug Analyzer 110V 220V compatible for 12V Vehicles How to use it: Step 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. Step 2. Connect to power supply. Step 3. Turn the key switch 4 clockwise to turn on tester, indicator 3 will light up, tester is now working at 1000rpm/min. Step 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. Tips: This link is compatible for 110V/220V power supply US PlugIf you need to buy 110V/220V EU PLUG, please note the incompatible formation of shipping EU PLUG when you take the order or