Comparing the old with the new calculator
Manuals; fx-991ES, fx-991EX
See also; The Calculator Guide introduction
And if you think this detail is OTT & the enthusiasm way too much, check out the resources available for GCSE/A-Level back in the 20th Century. I really appreciate every little feature of the calculator, I remember the hours spent looking up values in tables.
Comparing Calculators fx-991 ES v EX
Note to self; thanks to https://youtu.be/VVVZE34c-NE need to note there are now two x variable buttons. Top right hand corner new & probably easier to access.