The deviation of a rotating surface from its ideal axis or position.
Circular runout measures the variation of a single cross-section as the part rotates; total runout measures the whole surface. Both are checked with a dial indicator against a datum axis.
Runout is a composite control — it includes the roundness, concentricity and perpendicularity errors together, which makes it economical to specify where any of them would be unacceptable.
Specifying concentricity when runout would do. Concentricity is harder to verify and rarely necessary; runout captures the functional requirement more directly.
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