Casio fx 31. Dad bought this during his college days in 1978. Running flawlessly since 41 years now. I use it sometimes when I'm bored of using my phone. : r/BuyItForLife
calculadora casio scientific calculator fx-31 c - Buy Antique calculators on todocoleccion
File:Casio fx-31 with case and manual.jpg - Wikimedia Commons
Casio FX-31 – Vintage-Calculator.com
Casio fx-31 (1977) - Casio - LastDodo
Casio Fx-31 Calculator "please read" Casio memory-8F lot of 2 calculators | eBay