# Units The 7 definitions of the units library, each with its Epsil spelling, its MathJSON name, its signature and its full description. Each definition is listed under its Epsil spelling (the MathJSON name when it has none), with its signature in the engine's type syntax. The [Standard Library](/library/) page is the one-page index of every category. ## Definitions ### isCompatibleUnit MathJSON `IsCompatibleUnit` · `(value, value) -> value` Check if two units have the same dimension ### quantity MathJSON `Quantity` · `(value, value) -> value` A value paired with a physical unit ### quantityMagnitude MathJSON `QuantityMagnitude` · `(value) -> value` Extract the numeric value from a quantity ### quantityUnit MathJSON `QuantityUnit` · `(value) -> value` Extract the unit from a quantity ### unitConvert MathJSON `UnitConvert` · `(value, value) -> value` Convert a quantity to a different compatible unit ### unitDimension MathJSON `UnitDimension` · `(value) -> value` Return the dimension vector of a unit ### unitSimplify MathJSON `UnitSimplify` · `(value) -> value` Simplify a quantity unit to a named derived unit if possible