The standard deviation allows us to measure the precision of data by calculating its spread--that is, how far the numbers in the data set are from the mean. Calculating the standard deviation manually takes a lot of time, but thankfully the TI-83 can calculate it for you when given all the data points. You can then use the standard deviation to calculate the relative standard deviation, an expression of the data's precision as a percentage. The relative standard deviation makes it easier to compare the precision of more than one set of data.

Press the "Stat" button on your TI-83 calculator.

Move the cursor to "Edit" using the arrows, then select "1:Edit." You should see a spreadsheet with two columns, L1 and L2.

Clear any preexisting data by moving the cursor to the top of the column, selecting "Clear" and pressing "Enter."

Enter each X value into one row of the L1 column. If you have Y values as well, enter them in the L2 column.

Return to the "Stat" menu and select "Calc." Highlight "1-Var Stats" if you only entered data in the L1 column or "2-Var Stats" if you entered data in both columns.

Press "Enter." You should see a list of numbers, including the mean, standard deviation and five-number summary. Copy down the standard deviation, which is marked "Sx," and the mean, whose symbol is the x with a bar on top.

Divide the standard deviation by the mean and multiply it by 100. This number, expressed as a percentage, is the relative standard deviation.