Fibre Testing & Bale Management
Outside its calibration cottons, a micronaire conversion is extrapolation with a unit attached.
— %
Distance outside the calibration range as a share of its span; zero means the conversion is interpolation
The linear inflation of uncertainty with extrapolation distance is a deliberately crude penalty, not a statistical prediction interval — a real one widens faster than linearly and depends on where the calibration points sit within the range. Its purpose is to stop an out-of-range reading being reported to three figures as though it were interpolation. A negative maturity margin is the more serious flag: micronaire confounds fineness and maturity in one airflow reading, so two cottons of identical micronaire can differ substantially in both, and below the validity floor the regression separating them was never fitted. Calibration models are also fibre-specific. A model built on upland cotton standards does not transfer to extra-long-staple, to man-made staple, or to any blend of them, and no correction here makes it transfer — the honest action for an incompatible fibre type is a different method, not an adjusted number.
Fineness & Maturity Calibration Validity Converter — free, with the formula and a worked example, at Textile School.