Kip's right about the procedure, however, if you are looking for an out of round condition or a tapered conditon, you'll be there forever in a vailant attempt to get some hard data. Each measurement requires you to remove the tool and measure it carefully with a micrometer.

Far better would be an inside bore gauge that has the dial already attached to the unit. You set it in the bore.......seek out perpindicularity.......and read the dial. Then you move it up or down the bore..........or twist it 90 degrees.........and measure again. You can get 20 measurements on the bore within 10 minutes. With the Harbor Freight tool, 20 measurements will take you all day.

Sure, the Harbor Freight tool is a fraction of the price, but, what's your time worth?