Motion-Dimension command and Elements.
You must select three elements when you add a Motion-Dimension FB for a Rocker. They are:
|•||...followed by two Line sketch-elements.|
However, you may find you cannot select one of the Lines to complete the command.
This can happen when:
|•||there is already a Motion-Dimension FB at the Pin-Joint|
|•||the Point used by the Pin-Joint is not a child to Line radiating from the Pin-Joint.|
|•||the Pin-Joint that you select is not a Pin-Joint between the two Lines you want to select.|
Read this topic: Add Motion-Dimension.