Casio fx-991 Tricks: Useful Shortcuts and Functions | CalcNova
Casio fx-991 Calculator Tricks and Hidden Functions
The most useful fx-991 shortcuts are chaining with Ans, storing values in variables, re-running formulas with CALC, and toggling fractions with S⇔D. Each is explained below with an example. They are real, documented features, not secrets.
None of these are secret. They are documented features that many students never learn. We list only what Casio’s manuals describe and mark where models differ.
1. Chain calculations with Ans
Every result is stored in Ans. Start a new entry with an operator and the calculator inserts Ans for you. Example: calculate 3 × 4 = 12, then press ÷ 30 = to get 0.4, no retyping.
The ES PLUS manual also describes PreAns, the result before the last, usable in COMP mode. It is cleared when you leave COMP mode.
2. Store values in variables
There are nine variables: A, B, C, D, E, F, M, X and Y. Example: type 3 + 5, press SHIFT RCL (STO) then the A key, and A holds 8. Later, A × 10 gives 80. Store 0 to clear a variable.
Watch out: variables survive AC and power-off. If a later calculation behaves oddly, a stale variable may be the cause. Clear it, or use the Memory clear option in the reset guide.
3. Re-run a formula with CALC
The ES PLUS manual lists a CALC function. Type an expression using variables, for example 3A + B, press CALC, and enter values when asked. Casio’s example runs (A, B) = (5, 10) and then (7, 20): the results are 25 and 41. This saves retyping the formula for each case.
4. Solve for an unknown with SOLVE
The ES PLUS manual lists SOLVE for finding a variable that makes an equation true. It is a numerical method, so it may fail to converge or find only one of several solutions. Check availability for your exact model, and see our advanced functions guide. The CalcNova online calculator has no equation solver.
5. Switch between fraction and decimal
On Natural Display models, press S⇔D after a result to toggle between exact (fraction or root) and decimal form. 1/2 + 1/3 shows 5/6, and one press shows 0.8333…
6. Replay and edit earlier entries
The manual covers “Calculation History and Replay”. Use the cursor keys to step back to an earlier expression, edit one number and press = again. This is the fastest way to test several inputs.
7. nPr and nCr in one line
5 nPr 2 = 20 and 5 nCr 2 = 10. The operators are SHIFT functions on the keypad. See the functions guide for the layout.
8. Constants, conversions and extras
The ES PLUS manual lists scientific constants and metric conversion, plus rounding (Rnd), random numbers (Ran#, RanInt#), absolute value (Abs) and engineering notation. The ES PLUS C manual adds remainder, recurring-decimal, prime factorisation, GCD and LCM functions. Whether your fx-991EX or fx-991CW has each of these should be confirmed in its own manual.
Common mistakes
- Forgetting that the angle unit affects every trig answer.
- Trusting a stale variable or Ans from earlier work.
- Assuming a tip from one model works on another. Menus differ.
Frequently asked questions
- Are there hidden functions on the fx-991?
- Not in the sense of secrets. Every feature here is in Casio’s manual; the skill is knowing it exists.
- Does Ans survive turning the calculator off?
- Per the ES PLUS manual, yes: Ans, M and variables are kept when you press AC, change mode or turn it off.
- Do these tips work on my model?
- Basic ones such as Ans and variables are standard across the fx-991 family. For SOLVE, CALC and extras, check your model’s manual.