How do you go about doing a compression test. I tried to do it today, took all the spark plugs out, screwed in the tube in the spot where the spark plug goes, then hooked up the gauge, but then only cranked the motor one time. So the key was turned for probably about a half a second to a second, and the PSI for each cyliner read 70 to 75 psi on all 4 cylinders. From reading the numbers you posted I don't think I did it right? Am I doing something wrong, what is the proper way to do this?

After I figure out the psi, how will I figure out the ratio?