Dual Hole Car Spark Plug Tester Detector features two testing holes, allowing you to test two spark plugs simultaneously. If you suspect any spark plug is malfunctioning, you can compare and test both to make an accurate judgment.Usage: Test spark plug performance and ignition strength Application Range: 12V gasoline vehicle car spark plugs Car Spark Plug Test Principle: In the automobile ignition system, the high-voltage ignition coil generates a high voltage (10,000 volts or more). The spark plug directs this high voltage from the ignition coil into the engine cylinder, creating a spark between the electrodes to ignite the air-fuel mixture. The detector evaluates spark plug condition by measuring the strength of the spark.Car Spark Plug Tester Usage Notes: 1. Turn off power before inserting the spark plug. 2. The Spark Plug Tester is a high-voltage device; do not touch the spark plug during operation to avoid electric shock.Car Spark Plug Tester Instructions: 1. Insert the spark plug into tester hole 1 or 2. To compare a new and old spark plug, place the new spark plug in hole 1 and the old one in hole 2. 2. Connect to the power supply. 3. Turn the key switch clockwise to position 4 to activate the tester. The indicator light will illuminate, indicating the tester is operating at 1,000 RPM. 4. Continue turning the key switch clockwise to adjust the operating frequency between 1,000 and 5,000 RPM. Higher frequency results in stronger spark output.Main Unit Weight: 220g (excluding power adapter) Power Adapter: Input 100240V AC / Output 12V 1A DC Color: Black gray Material: Plastic Package Contents: 1 x Car Spark Plug Tester 1 x US Plug Adapter 1 x EU Plug Adapter Note: Light and display differences may cause slight variations between the product color in images and the actual item. Measurement error allowance is +/- 13 cm.