The unlimited undo feature of pcb-rnd allows you to recover from most operations that materially affect you work. Calling pcb_undo without any parameter recovers from the last (non-undo) operation. ClearList is used to release the allocated memory. ClearList is called whenever a new layout is started or loaded. See also Redo.

Note that undo groups operations by serial number; changes with the same serial number will be undone (or redone) as a group. See Atomic.