This Hi-Gauge Compression Tester is a tool for measuring and recording the pressure created by the piston in each cylinder. This information is used to diagnose faults in valves, pistons, piston rings, cylinder bores or head gaskets. Such tests are an excellent guide to general engine condition and can be used during routine engine servicing to give advance warning of developing problems or for fault diagnostics. Calibrated in BAR and Psi, this tool is suitable for petrol engines with 14/18mm spark plug ports.