The word accuracy in procurement discussions may refer loosely to accuracy, allowed error or repeatability. Used alone, it is insufficient. Acceptance documents should define the quantity, evaluation method, units and conditions rather than use one number for every aspect of measurement capability.
Answer three different questions
| Term used in discussion | Main concern | What it does not establish |
|---|---|---|
| Accuracy or closeness to a reference | Relationship between a measured value and the agreed reference | Reference method and uncertainty still matter |
| Repeatability | Dispersion of short-term repeated results under specified identical conditions | Absence of systematic offset |
| Resolution | Whether a change in the measured quantity produces a distinguishable indication | Dimensional error at that same numerical level |
See entries 2.13, 2.20, 2.21 and 4.14 of the JCGM International Vocabulary of Metrology. This table explains project communication; it is not an official translation of the vocabulary. Accuracy is qualitative. A contractual numerical threshold should specify the error measure or other performance characteristic being limited.
Closely grouped results can still be offset
Similar readings on repeated measurements of one workpiece indicate limited dispersion under the listed conditions. A consistent difference from the reference still requires investigation of calibration, reference features, temperature or algorithms. Re-clamping, changing operators and measuring on different days change the conditions. Record them separately rather than silently pooling them as one short-term repeatability group.
More display digits do not prove measurement resolution
Software can display more decimal places, but distinguishing actual changes also depends on noise, surfaces and processing. Pixel size, point spacing, display increments and physical dimensional error are different quantities. Specify which resolution is meant in quotations and acceptance tables rather than presenting display formatting as equipment accuracy.
Records needed for project acceptance
Record workpieces and reference values, device and algorithm versions, units, environment, clamping, repetition counts and individual results. Define separate checks for the agreed error evaluation, repeated-measurement statistics and measurement resolution, then assess suitability for the business requirements. This article provides no device-specific accuracy value, certification or acceptance conclusion.
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