From FreeCAD Documentation
- Optionally change the working plane.
- Make sure snapping is enabled. See Draft Snap Lock.
- If Draft Snap Dimensions is not active do one of the following:
- Press the button in the Draft snap toolbar.
- Press the button in the Draft snap widget.
- Choose a Draft or Arch command to create your geometry.
- Note that you can also change snap options while a command is active.
- Pick a first point. This snap option requires a previous point.
- As you move the cursor around temporary dimensions are displayed.