We all see measurement uncertainty on calibration certificates and often have little understanding of what it means or how it's calculated. In everyday life we will come across situations where we have doubt, if asked how hot you think it is you might say about 24°C, the about shows your uncertainty, you think it might be 24°C but without measurement you're not sure. Calibration uncertainty is putting some scientific endeavour behind this doubt.  Its giving a quantitative value to each element of doubt and to put a limit to the level of uncertainty. The inputs for doubt vary based on the kind of calibration being undertaken, with temperature it can be; the accuracy of the thermometer used to take the reading the calibration uncertainty on this thermometer the drift in the thermometer since last calibration the change in temperature within the environment whilst taking the measurement the ability to read the output correctly if the reading fluctuates plus many more Once all doubt inputs are accounted for and calculations made for each, an overall figure can be calculated that represents uncertainty. As a UKAS calibration house are required to calculate our uncertainty for every calibration we complete, this uncertainty is expressed on our certificates as a ± figure which is a factor of K=2, providing a coverage probability of approximately 95%. The uncertainty of our measurement underpins our whole calibration performance and is a key part of our documentation audited, annually, by UKAS For more information on Measurement Uncertainty see UKAS doc: M3003 - The Expression of Uncertainty and Confidence in Measurement