A compatible unit rule maps a specific set of operational attribute values for a given feature type to a particular compatible unit. Since unit rules are a type of metadata (i.e., data about compatible units), they provide a mechanism for searching by attribute values and for matching units to definitions of feature types.

Unit rules drive the Matched CUs page of the Units Catalog in the Design Assistant as well as the Compatible Unit Matches box on the Attributes page of the Placement Defaults dialog box. From this list, the user can select a unit for automatically assignment when the feature type is assigned.

Unit rules are managed with the Compatible Unit Rule Editor, which is accessed with the CU Rule Editor command on the Tools menu.