Found this incredible function on my Fx991EX if you press shift and Option button on left corner it creates a QR code that can be scanned with a phone to see graphing
Casio FX-991EX Classwiz Scientific Calculator 552 Function | eBay
Eddie's Math and Calculator Blog: Comparison: Casio fx-991EX Classwiz Vs Sharp EL-W516T
Amazon.com : Casio fx-991ES Plus 2 Scientific Calculator with 417 Functions and Display, Natural : Office Products
Casio FX-991EX Scientific Calculator FX 991 EX Classwiz 552 function New in Box | eBay
File:Casio fx-991EX.jpg - Wikimedia Commons
Working with Complex Roots with a Casio Classwiz fx-991EX | Cubic Equation Solving - YouTube
My FX-991EX seems to be stuck. It's not taking any inputs and not responding to reset button. : r/calculators
Original Casio Fx-991ex Advanced Scientific Calculator 552 Functions Engineering Students High School Lab Office Solar - Battery - Calculators - AliExpress
CASIO fx-991EX - Working with logs - YouTube
Amazon.com : Casio FX-991EX Engineering/Scientific Calculator, Black, 3" x 6.5" x 0.4" : Office Products