Model-Based Definition > Geometric Dimensioning and Tolerancing Advisor > GD&T Advisor > Establishing DRF (ISO) > Add DRF (ISO)
1. Display Datum from Targets Properties — For a datum from targets, this button launches a window that shows the values for the locating basic dimensions for the targets. This button is only enabled for datums from targets that are referenced in a fully constrained DRF.
2. Datum Feature Selector — Contains a filtered list of all applicable datum features and datum from targets.
3. Material Requirement Selector — For a datum features of size, you must specify a material condition modifier. This control is not applicable and disabled for non-size datum features
4. Add a Datum Feature — When defining a common datum from multiple datum features (e.g., coaxial datum features A-B), click this button to access the controls to an additional datum feature.
When specifying the datum features for a DRF, the Datum Feature Selector contains a filtered list of the applicable datum features so that only valid combinations of datum features are allowed. Keep in mind that not all datum features may be referenced as the primary datum in a DRF (see the notations in the 'Datum Feature?' column in Feature Descriptions).
Why does this dialog window sometimes appear automatically?
GD&T Advisor automatically adds a DRF to the model whenever you add a datum feature to the model that is capable of more fully constraining the part than any of the existing DRFs. If the added datum feature is a feature of size, a material requirement (<RFS>, Ⓜ, or Ⓛ) for that datum feature is needed to fully define the DRF. By default, the datum feature material requirement is made equal to the tolerance zone material condition modifier specified (if applicable) for the geometric tolerance applied to the feature. If the no geometric tolerance that requires a material requirement is applied to the feature (e.g., the first feature in the model) then this dialog window pops up automatically so you can specify the desired material requirement for the datum feature.