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A 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 $c=A_{\mathrm{seen}}/A_{\mathrm{target}}$ and observed pitting fraction ${\varphi }_{\mathrm{seen}}$ both refer to the same target surface. If unseen area has unknown pitting fraction $0\le {\varphi }_{\mathrm{unseen}}\le 1$, thenso the gear inspection missing-area bound isAt $c=0.8$ and ${\varphi }_{\mathrm{seen}}=0.02$, 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.^[ref] The audit and bound above specify an explicit measurement convention; they do not assert that the historical study used this digital-mask procedure.