circularity; roundness
Technical term used in engineering, manufacturing, and metrology to describe how close a shape is to a perfect circle. Often measured as a tolerance.
The circularity of this part is within 0.01 mm.
We checked the roundness of the machined cylinder using a circularity measuring instrument.
真直度 (straightness) is the analogous measure for how straight a line or axis is, compared to 真円度 for circularity.
Compound of 真 (true, perfect) + 円 (circle) + 度 (degree, measure). A modern technical coinage for 'circularity'.