Unbalance and eccentricity are interchangeable. We need to get used to the numbers we use here.

Let's put these numbers in context. The outer circle represents the typical diameter of a human hair 0.0035", about the same as the thickness of a sheet of paper. Next we have a circle diameter 0.001". Pretty well the normal limit of repeatability for any mechanical type of tooling. With new hydrogrip tooling you can get somewhere between 0.001 0.0001. We have a dot for 0.0001"-2.5 micron (The Hydrogrip system uses a high pressure grease gun to expand or contract a thin steel membrane).

We can usually balance down to a micron without much trouble until you move the rotor on the tooling! Of course, if you are balancing something that has its own shaft that is not a problem.

Finally, there is 1 microinch this is so small that you can't see it! We can't even measure it unless we use a high speed machine capable of spinning the rotor at 10,000 to 100,000 rpm.