Coping with Mistakes
ConstructSim Planner supports unlimited undo, which lets you undo "drawing" operations to recover from a mistake. You can use the View Previous and View Next view controls to scroll through viewing operations on a per view basis.
Note: A limitation on undoing is that unless you are recording the open DGN file's design history , you cannot undo operations made before the file was last closed. You see when you close or compress the file (including saving as), the undo buffer is emptied.