Uncertainty sized as one standard deviation and written u(x), whatever route produced it. Every component in a budget, whether from repeated data, a certificate or a spec, is converted to this form before combining. A certificate value of 0.8 mg at k = 2 becomes 0.4 mg, and a ±0.1 °C spec limit treated as rectangular becomes about 0.058 °C.
Convert everything to standard uncertainty before you square and add, half these lines are still at k equals 2.
Also heard as
- standard measurement uncertainty
- u
Do not mix it up with
- Expanded uncertainty: Standard uncertainty is one standard deviation; expanded uncertainty multiplies it by a coverage factor to give a wider interval.
Related terms
Combined standard uncertainty
The total standard uncertainty of a result, found by combining all input uncertainties through the measurement model.
Expanded uncertainty
Combined standard uncertainty multiplied by a coverage factor to give an interval with a stated coverage probability.
Type A evaluation
Putting a number on an uncertainty component by running statistics on your own repeat readings.
Type B evaluation
Sizing an uncertainty component from existing knowledge such as certificates, specs or resolution, with no new repeat data.
Standard deviation
The usual measure of scatter in a set of values, the square root of the average squared deviation from the mean.