Concentricity error

In an optical fiber, the concentricity error is the distance between the center of the two concentric circles that specify the cladding diameter[?] and the center of the two concentric circles that specify the core diameter[?].

The concentricity error is used in conjunction with tolerance fields to specify or characterize optical fiber core and cladding geometry.

Synonyms are: core eccentricity, core-to-cladding concentricity, core-to-cladding eccentricity, and core-to-cladding offset.

Source: Federal Standard 1037C