This paper will define surface irregularity for spherical surfaces, offer information on measurement methods for testing surface irregularities, and some specification guidelines.

1. SURFACE IRREGULARITY FOR SPHERICAL SURFACES

Irregularity is error in surface form relative to an ideal form. For spherical surfaces, irregularity is how much the actual surface deviates from the radius of curvature of an ideal or perfect best fit sphere (BFS), and accordingly may be called asphericity¹. BFS is chosen at minimum Root Mean Square (RMS) irregularity². Figure 1 shows a 2-D example of the relationship between ideal form and the actual surface...

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