1. It has two testing holes, you can test two spark plugs meanwhile and and if you suspect any spark plug works improperly you could compare and test to make accurate judgment. 2. Adjustable double hole car spark plug tester detector Ignition Plug Analyzer Diagnostic Tool 3. Usage: Test spark plug performance and ignition strength 4. Application Range: 12V Gasoline vehicles car spark plugs 5. 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).Close up the protective cover , then plug in the adaptor to the side socket , connect the tester to power supply. (3).Turn the key switch clockwise to turn on tester, indicator will light up green. (4). Continue to turn the switch clockwise, you can adjust the working frequency between 1000rpm to 6000rpm/min, The higher the frequency is set, the stronger the spark more.
