Various methods can be used to cancel errors until the latest correct operation if perform error manipulations.
Undo a Single Action
You can reverse to the last operation by pressing Undo button on the Standard toolbar or entering U on the command line. Some commands contain the Undo option, so you can enter u to reverse to the last operation without exiting the command. For example, when creating a line or polyline, you can enter u to undo the latest drawn line segment.
Undo Several Actions at Once
UNDO command help aborting multiple operations at a time.
When using UNDO command, system groups a number of operations assigned within Begin set and End set so that you can cancel all the steps as a group object at a time. Use Mark and Back to mark to enable users to cancel all the later operations since the marked step. If you use Back to mark or Number of steps to undo option, the drawing will be redrawn if necessary. This may happen to the end of UNDO command, and the frequency of redrawing can be different based on the option you select, for example enter UNDO 3 to redraw once, while enter U command three times to redraw three times.
Reverse the Effect of Undo
You can use REDO to reverse the effects of previous UNDO or U command. This command is equivalent with the REDO button on the standard toolbar.
Undo or Redo Actions Using Undo or Redo button
The Undo or Redo button on Standard toolbar are displayed in gray if there isn't any operations to undo or redo, at this moment this function is unavailable.
The Undo button is available as soon as you have operated a certain commands, click left part of this button to undo last manipulation performed previously. There is a pull-down list beside the undo button, click here to pop-up a list in which all of the possible operations are displayed, containing up to 6 commands within one list page, if more than 6 operations have been manipulated, you can drag the scroll bar on the right side of the list page to browse the commands.
The Redo button is available once you have manipulated undo. Like performing Undo operation, click the Redo button to perform the last Undo operation, while click the pull-down arrow to pop-up a list in which all of the manipulations available to perform Redo are displayed.
Move the mouse to select manipulations from the pull-down list of Undo and Redo button, highlight the items on which the mouse stays to illustrate how many items are selected among the manipulations from the top of the list page, and display a message at the bottom of the list to explain the number of items being selected. And then click the mouse or press ENTER directly to perform Undo or Redo command. Move the mouse to the top or button of the pull-down list box to enable it scrolling by itself, additionally you can press the direction key to select commands upwards or downwards.
Once you select BEgin set option when performing UNDO command, the manipulations displayed in the pull-down list beside the Undo button will be unavailable, at this time you can only undo the subsequent manipulations unless you perform the UNDO command again and select the End set option.
You can also use OOPS command to restore the deleted objects except for the objects deleted by PRUGE command. You can use OOPS to remove the selected block objects after performing BLOCK or WBLOCK.
Cancel a Command
You can click ESC to exit during performing command.
ERASE: Removes objects from a drawing
OOPS: Restores erased objects
REDO: Reverses the effects of previous UNDO or U commands
MREDO: Reverses the effects of several previous UNDO or U commands
U: Reverses the most recent operation
UNDO: Reverses the effect of commands
System Variables Reference
UNDOCTL: Stores a bitcode indicating the state of the Auto and Control options of the UNDO command