Measurement in Practice
People make measurements for many reasons: to make sure an item will fit, to determine the correct price to pay for something or to check that a manufactured item is within specification. In all cases, a measurement is only useful if it is suitable for the intended purpose...
Consider the following questions:
Do you know how accurate your measurement result is?
Is this accurate enough?
How strongly do you trust the result?
!!! These questions relate to the quality of a measurement. When talking about measurement quality, it is important to understand the following concepts: precision, accuracy and uncertainty, repeatability and reproducibility, tolerance, traceability and calibration etc.
Precision, Accuracy and Uncertainty
Precision is about how close measurements are to one another. Accuracy is about how close measurements are to the ‘true value’.
In reality, it is not possible to know the ‘true value’ and so we introduce the concept of uncertainty to help quantify how wrong our value might be.
The difference between accuracy and precision is illustrated here. The idea is that firing an arrow at a target is like making a measurement. Accuracy is a qualitative measure of how close a measurement is to the centre of the target – the ‘true value’. Precision is represented by a cluster of consistent measurements, but there is no guarantee that these are accurate.