KEDSUM Hour meter Tachometer 2 & 4 Stroke Small Engine Spark For Boat Outboard Mercury Applications for One Cylinder+2-Stroke / 2 Cylinders+2-Stroke / or Single Cylinder+4-Stroke / 2 Cylinders+ 4-Stroke / 4 Cylinders+ 4-Stroke gas powered engines It will show both engine RPM and hours of operation,Read up to 99,999 RPM Internal battery rated for 35,000 hour of operation (Not Replaceble ) Easy to install,Programmable maintenance interval setting.[IMPORTANT: The temperature must be lower than 176(80), otherwise burning out the unit] Can reset total hours and maintenance time, Wrap whole wires(NOT Stripped) around your spark plug cable for Five Times. Please Note: The induction wire needs to be distant from the high voltage generator and any other component capable of generating conflicting electrical noise.