Systematic & Random Errors

Errors are the inevitable consequence of making measurements, although perhaps a better description would be to use the word 'uncertainty'.

A systematic error is one which occurs with the same sign in every measurement, e.g. times measured on a slow running stop-watch. Finding and eliminating systematic errors is problematic, but it can often be achieved through experience in assessing whether a given result "makes sense", or by swapping the apparatus.

Random errors result from random fluctuations in the measurement as a result of apparatus or human intervention! Random errors can be assessed by making multiple measurements of the same observable. This not only reveals the presence of random errors, but also allows their magnitude to be estimated.

Precision & Accuracy

The terms accuracy and precision are often used synonymously, although this is incorrect.

The term precision is used to describe the statistical uncertainty of our results, i.e. it describes the extent of our random errors.

On the other hand, accuracy describes the extent to which our observations agree with the true value of the observable.

It is therefore possible to have an experiment that is very precise, in that it consistently gives the same result, but inaccurate in that this result disagrees with the correct answer because of systematic errors.