Model-Based Definition > Model-Based Definition > Working with Legacy Datums > Working with Legacy Datums
  
Working with Legacy Datums
A model created in Creo Parametric 3.0 and earlier may contain the following types of datums:
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Datum Types
Description
Set
Use to mark planes and axes. You can place it on datum planes and on dimensions.
Set Datum Tag annotation
This annotation is similar to a datum feature symbol. It is recognized by GTOL annotations in the same way that datum feature symbols are recognized by GTOL annotations. You can place a set datum tag annotation on datum planes, on dimensions, in GTOLs, or on geometry.
Impact of ASME and ISO Standards on Datums
Creo Parametric 3.0 and earlier uses the older versions of standards: ASME Y14.5, ISO 1101, and ISO 5459. In Creo Parametric 3.0 and earlier, you can place datums on axis systems or on nonreal geometry surfaces, and reference them from the GTOL frame.
Creo Parametric 4.0 and later uses more recent versions of these standards. As a result, you can only place datums on real geometry surfaces or on other annotations, as stacked annotations. You cannot reference legacy set datums from GTOLs. GTOLs support only set datum tag annotations and semantic datum feature symbol annotations. Therefore, you need to reestablish the connections between GTOLs that previously referenced set datums.