Review on Engine Compression Cylinder Pressure 0 300PSI by Tutcht Cobb

I bought this product to do a compression test on my 90hp Yamaha outboard. The first reading was 70psi/50psi/50psi on three cylinders. I ran a second test with similar results (50psi/55psi/50psi). Before taking the boat to the mechanic in the marina, I decided to try it with another tester. I rented one from Autozone and the readings were over 100psi across three cylinders. Save money and time by renting this tool from Autozone (renting is free!) or buy a better tool!