Concept of uncertainty
Measurement uncertainties and tolerances

The concept of uncertainty is relatively new in the history of measurement. For decades we've been calculating error, and it's important to understand the fundamentally different nature of the concepts of error and uncertainty.

It is now accepted that, once all known or suspected error components have been evaluated and the appropriate corrections applied, there is still some uncertainty as to the validity of the announced result (figure 1) (corrections are made to the best of our ability, but are never perfect).

The metrologist's aim is to announce a result close to the true value. To achieve this goal, he will reduce systematic errors by applying corrections. He will...