Roundness

Roundness is the measure of how closely the shape of an object approaches that of a mathematically perfect circle.

In geometric dimensioning and tolerancing, control of a cylinder can also include its fidelity to the longitudinal axis, yielding cylindricity.

Roundness is dominated by the shape's gross features rather than the definition of its edges and corners, or the surface roughness of a manufactured object.

In geology and the study of sediments (where three-dimensional particles are most important), roundness is considered to be the measurement of surface roughness and the overall shape is described by sphericity.

This is important in manufacturing, such as for crankshafts and similar objects, where not only the roundness of a number of bearing journals must be measured, but also their alignment on an axis.

A bent crankshaft may have perfectly round bearings, yet if one is displaced sideways, the shaft is useless.

A single trace covering the full rotation is made and at each equally spaced angle,