Core metrology · Foundation · Both
Measurement results and metrology fundamentals
Build a disciplined vocabulary for indications, results, error, correction, accuracy, precision, resolution, repeatability, reproducibility, and uncertainty.
Realistic time estimate
35 minutes total
- Study
- 13 min
- Worked example
- 5 min
- Field exercise
- 12 min
- Knowledge check
- 5 min
Estimates assume careful reading at roughly 175–200 words per minute, completing the worked example, carrying out the field exercise with the needed records or equipment, and answering all knowledge checks. Site procedures, equipment access, and deeper review may extend the time.
Define the measurand before measuring
A measurand is the quantity intended to be measured. A value without the quantity, unit, conditions, and method can be ambiguous. The same device may support several measurands depending on setup and procedure.
Technician actionState what is being measured, where, under what conditions, and in what unit before recording data.
Engineering noteConfirm that the measurement model and method actually produce the intended measurand rather than a convenient proxy.
Indication, result, error, and correction
An indication is the value supplied by the measuring instrument. A measurement result adds the quantity value and relevant information needed to interpret it. Indication error equals indication minus reference; correction is the negative of that error under the same convention.
Technician actionPreserve the original indication before correction, adjustment, or rounding.
Engineering noteDocument sign conventions and reference values so automated calculations cannot silently reverse correction.
Accuracy, precision, and repeatability
Accuracy is qualitative closeness to the true quantity value and should not be reported as a numerical result. Precision describes agreement among repeated indications under stated conditions. Repeatability is precision under the same conditions; reproducibility changes relevant conditions.
Technician actionUse repeat readings to describe observed spread, not to claim accuracy.
Engineering noteSpecify the precision condition—repeatability, intermediate precision, or reproducibility—before comparing data sets.
Resolution and significant digits
Resolution is the smallest displayed or discernible change. Extra decimal places added by software change formatting only; they do not create measurement information, reduce uncertainty, or improve accuracy.
Technician actionRecord the raw display as observed and report digits consistent with the method and resolution.
Engineering noteKeep guard digits during calculations, then round only the final result according to the controlled reporting rule.
Tolerance and uncertainty are different
Tolerance describes permitted product or process limits. Measurement uncertainty characterizes dispersion of values that could reasonably be attributed to the measurand. A result can be inside tolerance while the conformity decision remains uncertain near a limit.
Technician actionNever substitute instrument tolerance, process tolerance, or resolution for measurement uncertainty.
Engineering noteEvaluate uncertainty and the agreed decision rule when making or designing conformity statements.
Worked example
A pressure indicator reads 100.40 kPa against a 100.00 kPa reference. Error = +0.40 kPa and correction = −0.40 kPa. A 0.01 kPa display resolution does not prove ±0.01 kPa accuracy.
Field exercise
Select one instrument and write a complete measurement statement: measurand, indication, unit, reference, error, correction, resolution, and the uncertainty source you would need.
Knowledge check