Measurement, Test & Control Equipment worked example

Measurement Uncertainty Margin at 29% target uncertainty-to-tolerance ratio: a worked example

What does the result look like when target uncertainty-to-tolerance ratio reaches 29%? The full calculation is worked below with real intermediate numbers. Use when evaluating whether your measurement system has enough margin to make reliable pass/fail decisions, setting guard bands for test limits, or reviewing test adequacy ratios (TAR) during MSA studies.

The inputs for this scenario

  • Expanded measurement uncertainty (U): 12 units (unchanged)
  • Total specification tolerance band: 100 units (unchanged)
  • Target uncertainty-to-tolerance ratio: 29 % (raised for this scenario; the documented default is 25)

Working through the calculation

  • Applying the documented formula (Uncertainty margin = expanded uncertainty / total tolerance band x 100) to the inputs above produces each figure below.
  • At this operating point the engine returns 12 % for uncertainty-to-tolerance ratio, the number this scenario is built around.
  • At this operating point the engine returns 17 points for gap to target ratio.
  • At this operating point the engine returns 12 count for expanded uncertainty (u).
  • At this operating point the engine returns 100 count for total tolerance band.

How this compares with the baseline

  • Against the tool's baseline example, where target uncertainty-to-tolerance ratio sits at 25% and the headline result is 12 %, this scenario lands almost exactly on the baseline at 12 %.
  • A figure at this level is achievable when target uncertainty-to-tolerance ratio is genuinely sustained, not just peaked for a shift. It is a simple ratio, not a full guard-band or measurement-decision-risk model; it assumes the uncertainty and tolerance are stated on the same basis (same units, expanded U at the same coverage factor).

Results at a glance

  • Uncertainty-to-tolerance ratio: 12 % (headline result)
  • Gap to target ratio: 17 points
  • Expanded uncertainty (U): 12 count
  • Total tolerance band: 100 count

Run it with your numbers

  • Every input above is editable in the live Measurement Uncertainty Margin calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.