Read the instructions again today,remove one plug installed gauge crank engine over until needlle on gauge no longer moves, write down reading replace plug go to next cylinder and repeat. But just for giggles I removed all plugs and took reading, Got same reading as with the plugs installed, Also checked gauge by installing it in the stock 440 in my Daytona got a reading of 130 only checked one cylinder, but is the readings I felt I should be getting on the Challenger engine