Type A and Type B identify evaluation approaches. They are not interchangeable labels for random and systematic error.
Keep the method visible
Type A evaluation uses statistical analysis of measured values under defined conditions. Type B uses other information, such as a calibration certificate or authoritative specification. Either approach can contribute to an uncertainty budget; the label alone does not determine whether an influence is important.
A hypothetical budget classification
Imagine local repeated check readings provide one component, while a reference certificate supplies another. Classify the first by its statistical evaluation and the second by how its certificate information is used. Keep the actual data, assumptions and conversion to standard uncertainty beside both entries.
A systematic effect estimated from repeated data is not automatically Type B just because it is systematic. Likewise, a component reflecting variable behavior can be evaluated from external information. This example provides no complete weighing uncertainty budget.
Review the evidence before the label
Give each component a physical meaning, information source and calculation. Identify the condition and result to which it applies. Ask the analyst whether the same contribution appears elsewhere in the budget so that the classification exercise does not conceal double counting.
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 was the component evaluated? | Statistical data or other information |
| What evidence supports it? | Data, certificate or specification |
| Is it counted elsewhere? | Component dependency review |
Customer Questions
Does Type B mean unimportant?
No. Its magnitude and applicability still matter.
Are random effects always Type A?
No. The classification follows the evaluation approach.
Does the label replace the calculation?
No. Retain the actual information and conversion.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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