Also wrong adding in the 1 from the small dial because it isn't past it yet. The OP either rotated to zero with quite a bit of preload or the indicator is junk, as you'd expect that needle position from around .9 on the main dial, not just past zero. Either way, it's only total indicated runout that we're intereste in here. I concur, it .0055" Also, setting zero at the lowest point is valid because you're measuring total indicated run out that way. Setting it at a medium "datum" would still give the same numbers (assuming you zeroed with some preload and watched for the negative values), but what you did is spot on.