Got ahold of a Casio fx-991ex and CG-50 to match my Classpad II. I'm really impressed with them but there is something about the fx-991ex... (see comments) : r/calculators
Casio FX-991 EX Scientific Calculator with 552 Function Classwiz Spreadsheet | eBay
Amazon.com : Casio FX-991EX Engineering/Scientific Calculator, Black, 3" x 6.5" x 0.4" : Office Products
Which one is better, the Casio 991EX or the 991ES Plus? - Quora
Original Casio Fx-991ex Advanced Scientific Calculator 552 Functions Engineering Students High School Lab Office Solar - Battery - Calculators - AliExpress