Division sign

Its proper name is obelus. As a sign for division it first appears in Teutsche Algebra, Johann Rahn’s book of 1659. Long before that, copyists of ancient manuscripts had used an obelus to flag passages they suspected were corrupt or not genuine.

Today it lives mainly on calculator keys and in school sums. ISO 80000-2, which sets out mathematical notation internationally, says it should not be used for division, and in Norway, and until recently Denmark, the same mark has been used for subtraction.