Uncertainty and error in a measurement

Question

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.

Answer 1

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.