[Important Note] - This RPM signal pickup must be used with an automotive multimeter or oscilloscope that has a signal input function for engine system diagnosis and adjustment. [Perfect Engine Analyzer] - Inductive clamp lead is compatible with Automotive BT-770K, BT-90K, BT-6688B, and measures car frequency from 10 to 400Hz and tach range from 300 to 1200 RPM. [Versatile Clamp Hole] - Designed to measure secondary end conductors of high-voltage ignition coil spark; larger opening accommodates various spark plug wire sizes. [Easy Operating Steps] - Clamp the spark plug wire with the mark on the inductive pickup tool pointing toward the spark plug for engine speed measurement. [Notice in Measurement] - The distance between the spark plug and the clamp must be less than 3.93 inches (10 cm) during testing, and the ignition frequency of the engine ignition system must be between 10 Hz and 400 Hz. Operating temperature: -30 to 80C Relative humidity: Less than 80% Sensing Mode: Magnetic Induction Applicable Engine: Spark plug ignition gasoline engine Rotational Speed Measuring Range: 300 RPM - 1200 RPM Operating Instruction: Step 1. Connect the clamp to a spark plug wire with the mark on the tool pointing toward the spark plug. Step 2. Connect the plugs of the tool to the input terminals of the automotive meter. (The black plug should be connected to the COM jack of the automotive meter.) Step 3. Set the automotive meter to the corresponding measuring range. Step 4. Read the RPM value on the multimeter display. If no reading is received, unhook the clamp, turn it over, and reconnect. Color: Black Material: Plastic Package Contents: 1 x BT-705A Automotive Signal Pick-Up (Product markings may vary due to different batches, but this does not affect functionality) Only the above package content is included; other items are not included. Note: Light reflection and differences in displays may cause slight color variations between the image and the actual item. Measurement error allowance is +/- 1-3 cm.