1. Draw a line from the vertex where the green dot is below up to where the red dot is. A blue line should appear while you're drawing, indicating that you're moving direcly along the blue (vertical) axis. | 2. From there, draw another line along the ceiling to the far end. A green line should appear, indicating that you're moving directly along the green axis. | 3. Rotate around so you can see the other end, and draw a third line downwards. A blue line should appear again. |
![]() | ![]() | ![]() |