When chemists perform experiments, they often make a certain measurement more than once. It is not very common for replicate measurements to be exactly the same, so the set is averaged to determine the most appropriate value. In fact, it is possible to look at how far each individual piece of data strays from the central or average value to determine the uncertainty of the average (i.e. determine the standard deviation).

The average or mean (often noted as ) is the sum of all of the pieces of data divided by the number of the pieces of data. The statistician's way to mathematically represent the mean is as follows: