Uncertainty of measurement (UoM) is the doubt that exists about the result of any measurement.
For every measurement there is always a margin of doubt:
- How big is the margin? (width of the interval)
- How bad is the doubt? (confidence level - how sure we are the true value lies within that margin)
For example, the length of a certain stick measures 20 centimetres plus or minus 1 centimetre, at the 95 percent confidence level. This means we are 95 percent sure that the stick is between 19 centimetres and 21 centimetres long.
UKAS (SMTL's accreditation body) require laboratories to report the uncertainty of test results in test reports and test certificates under relevant circumstances. SMTL therefore report their UoM in an Annex to our test reports where this is relevant. This allows the client to assess the impact of the UoM against the specification.
If a client requires the UoM to be taken into account when we assess compliance with a limit, then the client must explicitely make this requirement known to SMTL when they sign the RFW (Request for Work contract). This can be done by amending the "ANY OTHER REQUIREMENTS" section of the RFW.