Handheld Computer Museum

I used this HP-21 calculator in college in the 1970s, and for years after. I chose HP because of their "reverse Polish notation" logic. For example, instead of entering "1 + 1 =" and then seeing the result displayed, you would enter "1 'enter' 1 +" and then the result would be displayed. Reverse polish notation becomes valuable when doing long calculations involving a number of different mathematical steps. It was fun when someone would ask to use my calculator and then they would ask "Where is the 'equals' button?" Eventually, the battery would not recharge, so I ordered a new battery back. Finally, the battery pack corroded inside the calculator, so it is now a historical artifact, unlikely to ever be revived.