The Obelus: History of the Division Symbol on Your Calculator

What Is the Obelus Division Symbol?

Did you know? That symbol on your phone’s calculator — the ➗ — has a name: the obelus. It has represented division for 365 years, since 1659, when Swiss mathematician Johann Rahn published his book Teutsche Algebra. Though many believe the first to use it for division was actually his teacher, John Pell.

The symbol didn’t catch on overnight. It spread first in England, then gradually across the rest of Europe. In some countries it was even used to denote subtraction for a time. Ultimately, its visual resemblance to a fraction — a line between two dots — is what sealed its fate as the division symbol.

The Ancient Origins of the Obelus Symbol

The symbol itself is far older than its mathematical use — by about 2,000 years. It was introduced by Zenodotus of Ephesus, a librarian and philologist at the Library of Alexandria. He used the obelus to mark dubious words or questionable passages in manuscripts arriving at the library, most notably in the works of Homer.

His students later refined the symbol into the form we recognize today. And yet people still say the humanities are useless.

How the Obelus Division Symbol Became Universal

From a proofreading mark in ancient Alexandria to the division key on every modern calculator — the obelus has had quite a journey. Its longevity across such different contexts speaks to how intuitive the symbol is: a horizontal line separating something above from something below, much like a numerator over a denominator.

Next time you tap ➗, you’re reaching back through centuries of mathematical notation history — and a little bit of Homeric scholarship too.