[Important Note]-This RPM signal pick up must works with automotive multitester meter or oscillograph with signal input function, for engine systems diagnosis and adjustment. [Perfect Engine Analyzer]-Inductive clamp lead is compatible to be used with for Automotive BT-770K, BT-90K, BT-6688B, and measure car frequency 10-400Hz and tach range 300-1200 RPM . [Versatile Clamp Hole]-To measure secondary end conductors of high voltage ignition coil spark, bigger hold is more useful for size of spark plug wires. [Easy Operating Steps]-Clamp the spark plug wire with the mark "" on the inductive pickup tool pointing to the spark plug for engine speed measurement. [Notice in Measurement]-The distance between the spark plug and the clamp of the inst ent must be less than 3.93 inch (10cm) during test, and the ignition frequency of the engine ignition system must be between 10Hz and 400Hz. Operating temperature: -30 to 80 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 of the inst ent to a spark plug wire with the mark on the inst ent pointing to the spark plug. . Connect the plugs of the inst ent to the input terminals of the automotive meter. (The black plug of this inst ent should be connected to COM jack of the automotive meter.) Set the automotive meter in corresponding measuring range. Then you can read the RPM value on the multimeter display. If no reading is received, unhook the clamp, turn it over and connect again. Colour:Black Material:Plastic Package Contents: 1 x BT-705A Automotive Signal Pick-Up(The words on the product due to different product batches, but it not affect the use Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.