# IfcUnitAssignment

_IfcUnitAssignment_ indicates a set of units which may be assigned. Within an _IfcUnitAssignment_ each unit definition shall be unique; that is, there shall be no redundant unit definitions for the same unit type such as length unit or area unit. For currencies, there shall be only a single _IfcMonetaryUnit_ within an _IfcUnitAssignment_.
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> NOTE A _IfcProject_ has a unit assignment which establishes a set of units which will be used globally within the project, if not otherwise defined. Other objects may have local unit assignments if there is a requirement for them to make use of units which do not fall within the project unit assignment.

> HISTORY New entity in IFC1.5.1.

## Attributes

### Units
Units to be included within a unit assignment.

## Formal Propositions

### WR01
Checks that the set of globally assigned units has each unit type (either of type _IfcNamedUnit_,_IfcDerivedUnit_, or _IfcMonetaryUnit_) defined only once.