The Casio FX-85MS is a scientific calculator that can handle regressive calculation, be used for standard deviation, and perform trigonometric calculations. It has a two line display and can recall the last formulas you entered. Basic use is simple, and the vast array of buttons makes it easier to use things like parentheses and fractions, as they often have a dedicated key.

Remove the FX-85MS's front cover by sliding it downwards and off. This can be attached to the back of the calculator, by sliding it upwards with the thin edge to the top.

Press "On" to switch the FX-85MS on. This button is located at the top right of the keypad, directly underneath the display screen.

Select the appropriate "Mode." For basic calculations, this is "Comp" mode, which is selected by pressing the "Mode" button followed by the number "1." The "Mode" button is located to the left of the "On" button. You can also set the FX-85MS into "SD" or standard deviation mode, and "Reg" mode for regression calculations. These are done by pressing "Mode" and then "2" and "3" respectively.

Input your desired calculation. For example, to input "6x(13-5)" you need to press "6," then "x" (located directly to the right of "6"), followed by the "(" key (located above the number "9") and then the sum "1," "3," "-" and "5." The minus key is located to buttons right of "3." Finally, input the ")" button and press "=" to see the answer: "48" will be displayed on the lower half of the display screen. You don't actually need to close the brackets if you're pressing "=" directly afterwards, the FX-85MS will close the brackets automatically and display the answer.

Press "Left" and "Right" on the off-circle navigational button to move the cursor through your calculation to correct any mistakes before pressing "=." When the cursor is underneath the number or symbol you wish to delete, press the "Del" button, which is the left of the two red buttons beside the "9" key. To replace the character, hold "Shift" and press "Del" before making your alteration. This procedure sets the FX-85MS in "Insert" mode, indicated by the change in cursor from "_" to the dotted outline of a square. The "Shift" button is located in the top left-hand corner of the keypad. You will see that "Ins" is written in yellow above the "Del" key. This is the button's "Shift" function, which many of the buttons have. These are the commands above the buttons written in yellow. The ones written in red are performed by holding the "Alpha" button and pressing the corresponding button.

Press "Up" on the navigation button to view your previous calculation. The FX-85MS recalls the formula and results of all of the calculations in your current session. This memory is wiped when you turn the calculator on or off and if you switch between calculation modes.