First put your calculator in stat ("s.d.") mode by typing MODE and then pressing the decimal point key. (When you are all finished, you can return your calculator to "computational" mode by typing MODE and then pressing the zero key. If you don't, normal arithmetic operations may result in errors.)

Clear out any previously entered data: SHIFT, AC.

Enter data as follows: Say you have one variable, with values 6, 5, 17, 2. You would type 6, M+, 5, M+, etc.

To get the mean, type SHIFT 7. (The answer you should get is 7.5 .) To get the standard deviation, type SHIFT 9. (Answer: 6.56 .)

(Note that your calculator also has an option for calculating s.d. using n instead of n-1. Don't use that option! In this example, you would get 5.68, which is pretty far off from 6.56.)

If there is a 2nd variable, you can calculate its mean and s.d. similarly, but don't forget to clear out all previous data first: SHIFT, AC.

Don't forget to hit MODE zero when your statistical calculations are trough.

The fx-250HA does not handle two variables simultaneously, so it will not calculate r nor least-squares.