Autodesk AUTOCAD 2006, Command Reference Manual, Page: 1264 / 1490

UNDO
Reverses the effect of commands
Standard toolbar:
Command line: undo
Enter the Number of operations to undo or [Auto/Control/Begin, End/Mark, Back]:
Enter a positive number, enter an option, or press ENTER to undo a single operation
UNDO displays the command or system variable name on the command line
to indicate that you have stepped past the point where the command was
used.
NOTE UNDO has no effect on some commands and system variables, including
those that open, close, or save a window or a drawing, display information, change
the graphics display, regenerate the drawing, or export the drawing in a different
format.
Number
Undoes the specified number of preceding operations. The effect is the same
as entering
u multiple times.
Auto
Groups the actions of a single command, making them reversible by a single
U command. When the Auto option is on, starting a command groups all
actions until you exit that command. You can undo the group of actions as
if it were one action.
UNDO Auto is not available if the Control option has turned off or limited
the UNDO feature.
Enter UNDO Auto mode [ON/OFF] <current>: Enter on or off , or press ENTER
Control
Limits or turns off UNDO.
Enter an UNDO control option [All/None/One/Combine] <All>: Enter an option or
press ENTER
All
Turns on the full UNDO command.
1240 | Chapter 22