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Tolerance Stack-Up: Worst Case vs RSS

Worst case adds all adverse limits and supports guaranteed interchangeability within the defined one-dimensional model. RSS predicts a narrower range only when contributors are independent, centred and suitably distributed.

Technical publication review required before indexing · Draft reviewed 13 August 2026

Engineering workflow

  1. Build a signed dimension loop from a consistent datum scheme.
  2. Use worst case for guaranteed boundary analysis.
  3. Use RSS only with evidence for its statistical assumptions.
  4. Include geometric, thermal and assembly effects where material.

Worked example

Three bilateral contributors of ±0.05, ±0.03 and ±0.02 mm produce ±0.10 mm worst case and ±0.0616 mm RSS.

Calculate a tolerance stack

Limitations and checks

  • A one-dimensional stack does not resolve geometric tolerance zones.
  • Correlation can make simple RSS non-conservative.

Relevant AccuTouch next step

Use the calculation as a screening input, then confirm the actual gauge, fixture, software or automation configuration.

Discuss a multi-gauging fixture

References