Place Guide Line between Two Points
Suppose you want to place a Guide Line between the endpoints of these two Walls:
1. Draw a vector to one of the endpoints.
2. Press the mouse button down to get the multi-choice Guide Lines (the cursor changes to a fist).
3. Move the cursor to the other endpoint. The cursor changes to a checkmark.
4. Release the mouse button: a Guide Line is placed between the two points.