For close tolerance measurements, select a tool that has a tolerance ratio of at least

For close tolerance measurements, select a tool that has a tolerance ratio of at least

• A. 4:1
• B. 2:1
• C. 8:1
• D. 1:1

Answer: (A)

The main idea is that measurement accuracy for close tolerances depends on how fine the tool’s own tolerance is relative to the tolerance of the part being measured. A tolerance ratio used here means how the instrument’s tolerance compares to the part’s tolerance. When you require at least a 4:1 ratio, the instrument’s tolerance is one quarter of the part’s tolerance, giving enough resolution to reliably detect small deviations near the tolerance limits. For example, if the part tolerance is ±0.010 inch (a 0.020 inch total band), a tool with ±0.0025 inch tolerance yields a 4:1 ratio. That means the instrument’s own uncertainty is much smaller than the allowable variation, so a measurement near the limits is still clearly distinguishable from the acceptable range. A 2:1 ratio would only halve that margin, increasing the risk that a small error from the tool could mask a real out-of-tolerance condition. A 1:1 ratio would provide no extra discrimination at all. An 8:1 ratio would be even more capable, but the requirement specifies a minimum of 4:1, making the 4:1 option the correct choice as the baseline standard.

The main idea is that measurement accuracy for close tolerances depends on how fine the tool’s own tolerance is relative to the tolerance of the part being measured. A tolerance ratio used here means how the instrument’s tolerance compares to the part’s tolerance. When you require at least a 4:1 ratio, the instrument’s tolerance is one quarter of the part’s tolerance, giving enough resolution to reliably detect small deviations near the tolerance limits.

For example, if the part tolerance is ±0.010 inch (a 0.020 inch total band), a tool with ±0.0025 inch tolerance yields a 4:1 ratio. That means the instrument’s own uncertainty is much smaller than the allowable variation, so a measurement near the limits is still clearly distinguishable from the acceptable range. A 2:1 ratio would only halve that margin, increasing the risk that a small error from the tool could mask a real out-of-tolerance condition. A 1:1 ratio would provide no extra discrimination at all. An 8:1 ratio would be even more capable, but the requirement specifies a minimum of 4:1, making the 4:1 option the correct choice as the baseline standard.