How+to+Calculate+Standard+Deviation+without+a+Graphing+Calculator

Say we have a bunch of numbers like 9, 2, 5, 4, 12, 7, 8, 11. To calculate the standard deviation of those numbers:
 * 1. Work out the mean (the simple average of the numbers)
 * 2. Then for each number: subtract the Mean and square the result
 * 3. Then work out the mean of **those** squared differences.
 * 4. Take the square root of that and we are done!