Closely grouped readings do not establish agreement with a reference. Retain both repeatability data and the reference comparison.
Identify which evidence is available
Repeatability concerns measurement precision under repeatability conditions. Bias concerns an estimate of systematic measurement error. A cluster of readings addresses consistency under the recorded conditions; comparison with a suitable reference addresses a different aspect of the measurement.
An invented check sequence
Imagine repeated indications 100.18, 100.20 and 100.19 g for an item whose applicable reference value is 100.00 g. The indications are closely grouped yet shifted relative to that reference. Reporting only their small spread would conceal the disagreement.
Reference uncertainty, method and use conditions still matter to interpretation. The simple numbers here are teaching data, not a complete bias estimate or an HM accuracy statement. More repetitions alone do not remove a shared systematic effect.
Keep the questions separate
Record the repeated values and conditions for the precision question. For the reference comparison, retain reference identity, value, uncertainty and the instrument relationship. Ask the technical reviewer whether correction or further investigation is appropriate; do not infer conformity from tight grouping alone.
Primary references: JCGM international vocabulary, JCGM international vocabulary.
Measurement review worksheet
This blank worksheet is for your own project. It contains no H M machine trial result.
| Question | Evidence to retain |
|---|---|
| How repeatable are the readings? | Repeated data under defined conditions |
| What reference is applicable? | Value, identity and uncertainty |
| Is a systematic effect indicated? | Reviewed comparison and correction approach |
Customer Questions
Can tight readings prove zero bias?
No. Consistency and reference agreement differ.
Do more repetitions remove a systematic effect?
No. Repetition alone does not remove it.
Does this example diagnose a real instrument?
No. It illustrates the two evidence questions.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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