6. Mistakes to avoid

6.1 Don't confuse measurement uncertainty with measurement error

In the VIM, measurement error is defined as "the difference between the measured value of a quantity and a reference value".

To illustrate the difference between "measurement error" and "measurement uncertainty", consider the following simple example.

Measuring a DC voltage with a high-performance voltmeter gives a result of 12,000 V, which can be considered very close to the true voltage value.

The same voltage is measured with a more ordinary voltmeter and the result is 12.20 V, with a measurement uncertainty of ± 0.05 V. In this case, it can be concluded that the systematic error (bias) due to the voltmeter at the 12 V point is + 0.2 V, but that...