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SESK: Stuff Everyone Should Know · sesk.info/eng-tolerance-definition

In measurement standards, what is a tolerance?

The allowed limits of error from the true value or performance.

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  1. The average of many repeat readings
  2. The smallest digit an instrument can show
  3. The limits of allowable error from the true value ✔

Why: No real device is perfect, so standards set how far off it may be and still pass. A part drawn as 25.00 mm plus or minus 0.05 mm passes anywhere from 24.95 to 25.05 mm.

Huh, didn't know that: NIST Handbook 44 supplies model tolerances for commercial scales and fuel dispensers.

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My tolerance for bad unit jokes is plus or minus zero.
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References

Answer: The limits of allowable error from the true value. No real device is perfect, so standards set how far off it may be and still pass. A part drawn as 25.00 mm plus or minus 0.05 mm passes anywhere from 24.95 to 25.05 mm.

  1. NIST Handbook 44, 2026 edition nvlpubs.nist.gov/nistpubs/hb/2026/NIST.HB.44-2026.pdf
    A value fixing the limit of allowable error or departure from true performance or value.
    Checked 2026-10-10.
  2. NIST Handbook 44: Current Edition www.nist.gov/pml/owm/nist-handbook-44-current-edition
    Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices
    Checked 2026-10-10.

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