= Gear inspection coverage audit
A \b[gear inspection coverage audit] records which parts of a tooth surface were eligible for observation, which were excluded and why. It accompanies a <gear pitting area fraction> or <gear inspection common-region comparison> so that a numerical damage statistic can be interpreted against the area actually inspected.
A useful record retains the original image, <gear pitting inspection mask>, surface-coordinate map from <image registration>, represented pixel areas and exclusion reasons. Shadow, occlusion and an out-of-frame edge are different from a visible region classified as intact. An audit also distinguishes changes in viewing coverage from changes in the <image segmentation> rule.
An original calculation shows how missing area limits interpretation. Let inspected fraction $c=A_{\rm seen}/A_{\rm target}$ and observed pitting fraction $\phi_{\rm seen}$ both refer to the same target surface. If unseen area has unknown pitting fraction $0\le\phi_{\rm unseen}\le1$, then
$$
\Phi=c\phi_{\rm seen}+(1-c)\phi_{\rm unseen},
$$
so the <gear inspection missing-area bound> is
$$
c\phi_{\rm seen}\le\Phi\le c\phi_{\rm seen}+1-c.
$$
At $c=0.8$ and $\phi_{\rm seen}=0.02$, the whole-target fraction lies between $0.016$ and $0.216$ without further information. This is a deterministic range over missing data, not a statistical confidence interval. A small observed fraction does not alone establish a small whole-target fraction.
For repeated inspections, record areas visible only initially, only later and at both times. A common-region result can be valid for its intersection while becoming less representative of the full target if a damaged edge is systematically lost. Increasing pixel count inside the retained region does not recover information about the missing region.
The primary NASA gear-endurance study connected inspection history to vibration and oil-debris observations, illustrating the importance of tying a damage interpretation to physical inspection rather than a signal label alone.<Gear Fault Detection Effectiveness as Applied to Tooth Surface Pitting Fatigue Damage by David G. Lewicki and others>[Printed pp. 2–5, test procedure, inspections and monitoring comparisons]{ref} The audit and bound above specify an explicit measurement convention; they do not assert that the historical study used this digital-mask procedure.
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