In order to calculate the standard deviation of a set of numbers your first step is to discover the mean. The mean is the sum of all of the numbers divided by the quantity of numbers. As an example, the mean of 2,3,5 and 6 would be 4, because the numbers total 16 and there are 4 of them 16/4=4. Once you have the mean you will subtract that number from every number in the list, this will result in

. a new set of numbers (negatives are ok). Square that list of numbers, which you will do by multiplying the numbers by themselves. Add all four of your new numbers together, then divide that total by one less than the amount of numbers in your list. You can find more information here: http://hubpages.com/hub/stddev