Casio Calculator Buttons and Functions Explained | CalcNova
Casio Scientific Calculator Functions Explained
The main keys on a Casio scientific calculator are AC, DEL, SHIFT, ALPHA, the trig and log keys, Ans and the memory keys. Below, each one is explained with a worked example, plus where the fx-991ES PLUS, fx-991EX and fx-991CW differ.
SHIFT, ALPHA and the keypad layout
Most keys do more than one job. The main label is on the key; the gold text above it is the SHIFT function and the coloured text beside it is the ALPHA function. Casio’s guide describes it the same way: pressing SHIFT or ALPHA followed by another key runs the alternate function printed above that key. An indicator on screen shows when SHIFT or ALPHA is active, and it clears after the next key press.
Example: SHIFT sin gives sin-1, the inverse sine.
AC, DEL and clearing
| Key | What it does |
|---|---|
| AC | Clears the current entry or result screen. Does not touch settings or stored memory. |
| DEL | Deletes the character at the cursor so you can fix one mistake. |
| SHIFT AC | Turns the calculator off (the ES PLUS guide marks this as OFF). ON turns it back on. |
| SHIFT 9 | Opens the reset menu on ES PLUS and EX. This one erases data; see our reset guide first. |
Powers, roots, fractions, scientific notation
- Square and general power: use the x² key for squares and the ^ key for any exponent. 210 = 1024.
- Roots: the square-root key gives √49 = 7. The SHIFT function of the root key gives other roots, for example the cube root of 27 is 3.
- Fractions: enter 1/2 + 1/3 using the fraction key and the result shows as 5/6. On Natural Display models the S⇔D key toggles between fraction and decimal form.
- Scientific notation: use the ×10x key. The speed of light, about 3 × 108 m/s, is entered as 3, then ×10x, then 8.
Trigonometry and angle modes
The sin, cos and tan keys work in whichever angle unit is set: degrees, radians or gradians. Check this first. With degrees set, sin 30 = 0.5. With radians set, the same keys give a very different answer, because 30 is read as 30 radians. Change the unit in Setup (on the ES PLUS, SHIFT MODE).
Inverse functions (sin-1, cos-1, tan-1) sit above the same keys and are reached with SHIFT. They return an angle in the current unit.
DMS: the ° ′ ″ key enters degrees, minutes and seconds. 1°30′0″ equals 1.5°. Our DMS guide covers conversions in depth.
log and ln
log is base 10: log(1000) = 3. ln is the natural logarithm, base e: ln(e) = 1. They give different results for the same input, so use the right key for your problem. The same pair appears on the CalcNova online calculator if you want to check a value.
Ans and memory
- Ans holds the last result. Press × or + right after a result and the calculator inserts Ans for you. Example: 3 × 4 = 12, then ÷ 30 gives 0.4.
- Variables: there are nine named A, B, C, D, E, F, M, X and Y. Store with SHIFT RCL (STO) and a variable key: 3 + 5, store in A, then A × 10 gives 80. Storing 0 in A clears it.
- M is the independent memory: M+ adds a result to it and SHIFT M+ (M-) subtracts. An “M” indicator shows when it is non-zero.
Per Casio’s ES PLUS guide, Ans, variable and M contents survive pressing AC, switching mode and powering off. Only a memory clear or reset erases them.
nPr, nCr and factorial
Permutations count ordered selections and combinations count unordered ones. nPr and nCr are SHIFT functions printed above keys; check your keypad. Enter the first number, the nPr or nCr operator, then the second.
| Expression | Meaning | Result |
|---|---|---|
| 5 nPr 2 | 5 × 4 | 20 |
| 5 nCr 2 | 5! / (2! × 3!) | 10 |
| 5! | 5 × 4 × 3 × 2 × 1 | 120 |
What differs between models
| Feature | fx-991ES PLUS | fx-991EX / fx-991CW |
|---|---|---|
| CALC, SOLVE, integrals, derivatives, Σ | Listed in the manual | Check your model’s manual |
| Complex, STAT, BASE-N, equation, matrix, table, vector | Listed in the manual | Check your model’s manual |
| Reset path | SHIFT 9 | EX: SHIFT 9. CW: Settings menu |
The ES PLUS column comes from Casio’s function list; we have not yet confirmed the same list line by line for the EX and CW, so confirm before relying on it. A separate guide on shortcuts and tips goes further.
Frequently asked questions
- What is the difference between AC and DEL?
- DEL removes one character; AC wipes the whole entry. Neither affects stored memory.
- Why is my sine answer wrong?
- Almost always the angle unit. Check Deg/Rad/Gra in Setup.
- Do all fx-991 models have the same functions?
- No. Models share a core but differ in menus and extras. Check your manual.