I do not find a clear and simple explanation of the difference between uncertainty and error of a measurement.

Basically, in a measurement, uncertainty is defined as the standard deviation of the distribution of a large number of measured values. According to this concept, we may state that:

Result = Measured Value + Uncertainty

My question is: why is it different from an error? If I say that a certain device can measure power with 1mW of uncertainty, I intuitively think that I can make an error of 1mW on my measurement.


Uncertainty is the amount of deviation in the reading that we have no control over. There is nothing we can do about it other than use a better measuring instrument. A scale for example has an uncertainty of +/-1mm. The only way to overcome this is to use something like a vernier caliper.

When we talk about error, we refer to a deviation which can be measured. Zero error, parallax error are some examples. The error in an instrument is usually compensated for in the final reading.


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