Gunson G4101 Hi-Gauge Compression Tester is the perfect tool for measuring and recording the pressure created by the piston in each cylinder. Then you can diagnose faults in valves, pistons, worn piston rings, oversize cylinder bores or head gaskets. Gunson Hi-Gauge Compression Tester can also help you to diagnose the cause of excessive oil consumption. By comparing readings across the cylinders, you can determine if the gasket is sound, or if leaking valves or piston rings are at fault. Hi-Gauge Compression Tester has a flexible high pressure hose and fits all 14mm and 18mm spark plug holes. Calibrated in imperial and metric pressure values (BAR and PSI). Complete with trouble shooting guide and instructions.