Keep Left Mouse button pressed for draw any number of Helpers Lines! ;)
And read ToolTips for see if you draw an Perpendicular one!



Function active say Cube
Right or Left button! ;) Function active before first point of the Function, after first Point of the Function Cube, before last point of the function Cube! ;)



For Keep Helper lines and other things...
http://kyticka.webzdarma.cz/3d/moi/#KeepCLine