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Casio FX 991 DEX - Instruction

Casio FX 991 DE X - Quick introduction to operation

On these pages you will find instructions for the Casio fx 991 DE X. We are orienting ourselves to the requirements from the 6th or 7th grade at community schools and grammar schools. This calculator is mainly used there.

CASIO is a registered trademark!

This website has been compiled to the best of our knowledge. Therefore, or despite this, we cannot accept any liability for any incorrectly reproduced content. It is best to try out all the examples yourself with your computer.

Almost all important functions of the calculator are discussed in the individual sections. Depending on the type of school, however, it may be that one or the other topic is only dealt with in passing or not at all. 

If you notice a topic that is still missing, write us an e-mail.

Casio fx 991 DE X - The calculator at a glance

Casio fx 991 DE X - The scientific calculator

The CASIO FX 991DEX is the top scientific, non-programmable calculator from the manufacturer CASIO. It can be used up to the Abitur and even beyond. Anyone who likes to work with Casio calculators will make a very good choice with this calculator.

Our recommendation!

Casio 991 DEX - Function overview

This brief overview of the Casio fx 991 DE X shows you the variety of functions, some of which we cover in individual chapters.

  • 696 functions
  • 47 scientific constants
  • 164 Unit conversions
  • 24 clamp levels
  • Fractions: 2 modes
  • Angle dimensions DEG/RAD/GRAD
  • Conversions between >DEG/>RAD/>GRAD
  • Coordinate conversion Pole ÷ Rec
  • trigonometric functions sin/cos/tan/sin-1/cos-1/tan-1
  • hyperbolic functions sinh/cosh/tanh/sinh-1/cosh-1/tanh-1 
  • Exponent, log, In, 10x,ex
  • Mathematical functions √, x2, x-1, 1/x, x!, √, xy, √, x1/y
  • Calculations in base n (hexadecimal/decimal/binary/octal)
  • logical operators (AND/Or..)
  • Calculations in the sexagesimal system
  • Percentage calculation
  • Residual function
  • Prime factorization
  • technical notation ENG/ENG
  • Calculation with technical symbols
  • Calculation of complex numbers
  • Random Number Generator
  • Integer random numbers
  • Calculation of minimum or maximum of a quadratic function
  • ggT/kgV function
  • Base-N calculations
  • Verify" function
  • Table of values
  • Periodic decimal fraction
  • Matrix calculation / vector calculation: 4×4
  • REF/RREF function
  • Equation calculation
  • Inequality calculation
  • Summation of ∑x, ∑x2
  • Summation of ∑x, ∑y, ∑x2, ∑y2, ∑xy
  • Standard deviations f. grouped and ungrouped values
  • Distribution functions (normal distribution, inverse normal distribution, binomial distribution, Poisson distribution)
  • Regression analysis
  • Permutation (nPr), Combinatorics (nCr)
  • numerical integral calculus
  • numerical differential calculus


  • Menu language: German
  • QR code function
  • Spreadsheet
  • Automatic switch-off
  • same-operator emulator software: optional
  • Power supply: solar + battery
  • Battery type: 1 x LR-44
  • Size (H x W x D mm): 1.1 x 77 x 165.5
  • Weight: 90 g

The individual functions explained in detail

Casio calculator: Use the buttons to access the individual topics of operation of the CASIO 991 DEX.