GIFSQ Tools · Module 15 — Metrology, Validation & Laboratory Accreditation · Tool 288 of 500
Analyse repeatability (same sample, same operator, same equipment, short time): mean, standard deviation, relative standard deviation and the repeatability limit r of ISO 5725.
Try sample values — fills the form with the worked example below.
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Mean
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Standard deviation (sᵣ)
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RSD (%)
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Repeatability limit (r)
Equation: Mean = Σx ÷ n. Sample SD sᵣ = √[Σ(x − mean)² ÷ (n − 1)]. RSD (%) = sᵣ ÷ mean × 100. Repeatability limit r = 2.8 × sᵣ.
Method: Repeatability conditions per ISO 5725-2 (accuracy of measurement methods and results): identical test items, same operator, same equipment, same laboratory, short time interval. Two results differ by more than r in only about 1 case in 20 when the method is in control.
Assumptions: the replicates are independent and from one stable sample; the results are approximately normally distributed.
Limitations: repeatability is the smallest precision component — it excludes day-to-day, operator and laboratory effects, so it always looks better than reproducibility.
Rounding: mean and SD to 2 decimal places; RSD to 2 decimal places; repeatability limit to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Repeatability conditions per ISO 5725-2 (accuracy of measurement methods and results): identical test items, same operator, same equipment, same laboratory, short time interval. Two results differ by more than r in only about 1 case in 20 when the method is in control.
Assumptions: the replicates are independent and from one stable sample; the results are approximately normally distributed.
Limitations: repeatability is the smallest precision component — it excludes day-to-day, operator and laboratory effects, so it always looks better than reproducibility.
Rounding: mean and SD to 2 decimal places; RSD to 2 decimal places; repeatability limit to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Replicates 10.1, 10.3, 10.2, 10.4, 10.2, 10.3 mg/kg: mean = 10.25, sᵣ = 0.10, RSD = 1.02%, repeatability limit r = 2.8 × 0.10 = 0.29 mg/kg.
Enter values above to see results.
If two repeat results differ by more than r, repeat the determination — the difference is unlikely to be chance alone. Tool 288 of 500 — GIFSQ
