Yarn Testing
Imperfections live in the tail of the distribution, so they move far faster than CVm does. A point of evenness is never a point of imperfections.
— per km
From the normal tail at the thin threshold
A normal-tail model is a useful first approximation and no more: real yarn faults cluster from drafting waves and periodic mechanical defects rather than arriving independently, so measured imperfections usually exceed this — sometimes by a lot. Compare against Uster Statistics for the count and process rather than treating the prediction as a specification.
Yarn Evenness CVm% to Thin & Thick Place Predictor — free, with the formula and a worked example, at Textile School.