Scientific Casio Calculator FX-991CW: The latest improved model of the FX-991EXLCD display is the Casio FX-991CW. There are nine variable memories. keys that don't stick. 32 + 10 + 2-digit screen. automatic shutdown. There are 540 functions. decimals that repeat. prime factorization. logic in algebra. analysis of regression. functions of statistics. exaggerated. There are 24 parenthesis levels. Met