Selecting a Point
When you choose a command that requires you to select points, red dots appear on the model that indicate where selections can be made. (If you do not see the red dots, you may want to go to the 3D Viewer Settings page and select the Points Visible on Picking check box.)
Red crosshairs indicate when the pointer is properly positioned over a point. A yellow dot indicates that you have successfully selected a point.
Selecting an Edge or Arc
Some 3D Markup Dimension commands, such as Edge Length and Arc Diameter, require you to select an edge or arc that already exists on the model. When the pointer is properly positioned over an edge or arc, the line or arc is highlighted.
It's easy to determine the volume, surface area, center of mass, bounding boxes, and weight of your model or part: Right-click an item listed in the assembly tree or on a model or part in the viewport to view the assembly context menu. Select Calculate, then select a function. See Assemblies and Parts in a 3D Scene and Assembly Context Menu for more information.