Which statement best describes the meaning of a 4:1 tolerance ratio when selecting a measurement tool?

• A. The tool tolerance is four times worse than the feature tolerance
• B. The tool tolerance is four times better than the feature tolerance
• C. The feature tolerance is four times better than the tool tolerance
• D. The tool tolerance equals the feature tolerance

Answer: (B)

When choosing a measurement tool, you want the tool’s tolerance to be smaller (more precise) than the feature’s tolerance by a stable factor. A 4:1 tolerance ratio means the tool’s tolerance is four times better than the feature’s tolerance—the tool can measure with four times less allowable error than the feature permits. In other words, the tool’s uncertainty is a quarter of the feature’s tolerance.

For example, if a feature tolerance is ±0.010 in, a 4:1 ratio implies selecting a tool with around ±0.0025 in tolerance (or better). This provides enough measurement headroom so that the instrument’s own inaccuracy doesn’t mask whether the feature meets spec.

So the best description is that the tool tolerance is four times better than the feature tolerance. The other options describe the tool as less precise, or the tolerances as equal, which would weaken the measurement capability or misstate the relationship.