Standard Deviation Standard Deviation Lower case sigma means 'standard deviation'.
Capital sigma means 'the sum of'.
It is useful in comparing sets of data which may have the same mean but a different range. However, the second is clearly more spread out. If a set has a low standard deviation, the values are not spread out too much. Now, subtract the mean individually from each of the numbers in the question and square the result. Then type in the first value, press 'data', type in the second value, press 'data'.