What ∶ means
It reads “is to” between two compared quantities. In 3 ∶ 2, the sign states a relationship; calculating 3 ÷ 2 is a separate step.
No one invented the finished sign: ratio notation evolved as compact writing for ratios and equal proportions. Oughtred published a related form in 1631; Wing used A:B::C:D in 1651, linking equal ratios with ::. The single colon then gained ground for one ratio, while Leibniz used it for division in 1684. The sources do not establish a separate cross-cultural meaning for ∶.
Ratio symbol vs colon?
Use ∶ for a relation; use : for punctuation. Unicode treats the mathematical colon as an operator, so typesetting can space it on both sides. Fonts may make the marks nearly identical, but software can preserve the distinction.
Technical mathematical notation, not casual punctuation.
Questions people ask
1Why does ∶ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ∶
∶\2236Codes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.