Answer:
Standard deviation is a statistical tool used to determine how tight or spread out your data is. In effect, this is quantitatively calculating your precision, the reproducibility of your data points. Here's how you find it:
1). Take the average of all the data points in your set.
2). Find the deviation of each point by finding the difference between each data point and the mean.
3). Add the squares of each deviation together.
4). Divide by one less than the number of data points. If there are 20 data points, divide by 19.
5). Take the square root of this value.
6). Done.