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CASIO fx-1000 Scientific Calculator -I believe this one is highly collectible
Amazon.com : Casio FX-260 Solar Scientific Calculator School Version (Fraction Key is Not Operable) : Office Products
Amazon | Casio fx-115ESPLS2 White Advanced Scientific Calculator with Natural Display | 関数電卓 | 文房具・オフィス用品
Amazon.com : Desktop Calculator Large LCD Display 12 Digit Number Handheld Portable Pocket Basic Calculator with Big Soft Sensitive Button, Battery and Solar Powered, for Office Home School Use(OS-6M) : Office Products