Model-Based Definition > Geometric Dimensioning and Tolerancing Advisor > GD&T Advisor > Using Tolerance Feature Dashboard > Tolerance Feature Dashboard - Geometric Control Properties > Datum Reference Frame Selection
Datum Reference Frame Selection
Why are some of my DRFs not listed?
Not all DRFs are available for each geometric tolerance. GD&T Advisor limits the selection of DRFs to those that are compatible with the requirements of the geometric tolerance. For example, a parallelism tolerance must reference a datum reference frame whose primary datum is parallel to the feature. A DRF whose primary datum is not parallel to the toleranced feature would not be compatible (or available) for a parallelism tolerance. If a DRF is not listed, the DRF is not compatible with the geometric tolerance.
If you do not want to use any of the DRFs listed, you can:
Add a DRF if there are applicable datum features available.
Select a different geometric tolerance for which there is a compatible DRF.
How do I decide which DRF to select?
The drop-down box shows several DRF choices. The DRFs listed are all of the DRFs that are compatible with the geometric tolerance. The best DRF is the one that supports the functional relationship you are establishing.
The way to decide which DRF to select is to first have a clear understanding of the functional relationship you are establishing. Then, select the DRF based on that functional relationship. For example, if the functional relationship is to locate a hole relative to the outside surfaces of the part, then the datum features that are the outside surfaces should be selected as the DRF.