This applies to features that should be centered relative to a datum.
While "m" handles size, handles shape. ISO 2768-2 defines four classes: H, K, L, and (formerly E). Class "K" is the standard medium precision for form tolerances. Tolerance Iso 2768 Mk Pdf
The ISO 2768 Mk standard acts as a universal language between design offices and machine shops. This applies to features that should be centered
Circular run-out limits the composite errors of concentricity and circularity when a part is rotated around an axis. Under class k, the maximum permissible circular run-out is . Tolerance Iso 2768 Mk Pdf