Proportion

The Proportion at U+2237 is a mathematical relation sign used to state that two ratios are equal, essentially “as is to, so is to.” It is part of the Mathematical Operators block and functions as a compact symbol for proportional relationships rather than as an arithmetic operator. Its main use is in mathematics, especially older or formal notation for ratios: a ∷ b ∷ c ∷ d can express a:b = c:d, read “a is to b as c is to d.” In school algebra and geometry, the same idea is more commonly written with a colon and equals sign, as in a:b = c:d, but the single proportion sign still appears in reference works, scanned textbooks, and symbolic math material. The sign is also encountered in logic-style and dictionary-style notation where analogy or correspondence is being emphasized, such as “hand ∷ glove ∷ foot ∷ shoe” to show matching relationships. It should not be confused with the ratio sign ∶ or the double colon ∷ used in some programming languages and linguistic notation, which may look similar but carry different meanings.