standard deviation
calculate mean of a data set:
1. Turn calc. on or press MODE SeTUP
2.Press 3 for STAT
3. Press 1 for VAR
4.Enter values for X column
5. When done entering press SHIFT 1
6.Press 5
7.Press 2 to calculate the mean
8.Press =
i did not come up with this explanation myself i found it on a website called fixya.com so I'm not taking credit for the answer but it works.