I did not know that yesterday!

While researching this question, we happened upon a word that made us feel old: vintage. It's hard to believe that our trusty math buddy is now considered vintage machinery.

According to Vintage Technology, both buttons are a way to clear or cancel an entry. The C button will clear all input to the calculator. The CE button clears the most recent entry, so if you make a mistake in a long computation, you don't need to start all over again.

Exactly when calculators began to use these buttons is hard to say. The Vintage Calculators Web Museum provides a timeline that seems to show that the Friden EC-130, which was introduced in 1964, included "clear entry" and "clear display" keys (as did its successor, the EC-132). Those may not be the exact C and CE keys we see today, but it sounds like they performed the same function.

Our nostalgia for the calculator led us to check out even older models -- just for fun. The futuristic sounding Comptometer, invented in 1884, definitely wouldn't fit into a pocket. And it looks like you could catch your tie in the 1874 Odhner. We'll stick with the credit-card-size models. They're less of a load.

Source: ask.yahoo.com