UNDO command

The UNDO command is used to give up the effect of operations.

Command Access:

Command : UNDO

Command Prompts:

Enter the number of operations to undo or [Auto/Control/BEgin/End/Mark/Back]<1>:

Function Description:

In the command prompt line, it will display commands and system variable names that used before.
Note: The UNDO command will be invalid for some commands and system variables, for example, open, close, or save viewport or graph, display information, change the display mode, regenerate graphics or export in different formats.

Relative Glossary:

Number : Specify number of operations to undo. It is equivalent to input U several times.
Auto : If the "control" option has turned off or restricted some functions of UNDO, the "Auto" option will be disabled.
Control : Restrict or turn off the UNDO command.

All : Turn off all UNDO command.
None : Turn off the U and UNDO commands, give up any information of UNDO in previous operation. The UNDO button on the "STANDARD" tool bar is disabled.
When the "None" or "One" is valid, the "Auto", "Begin" and "Mark" options are disable.
If trying to use UNDO command under the "None" status, it will display the following prompt:
Enter an UNDO control option [All/None/One/Combine/Layer] :
One:
Limit the UNDO command as a single step.
When the "None" or "One" option is valid, the "Auto", "Begin" and "Mark" options are disable.
When the "One" option is valid, the main prompt of UNDO command is one step of UNDO and displays "control" option.
Combine:
Control whether to combine multiple and continuous ZOOM and PAN commands into a single step for UNDO and REDO operations.
Note: the ZOOM and PAN commands that started from menu are not combined, they are separate operations.
Layer:
Control whether to combine layer dialog operations into a single UNDO operation.

Begin, End:
Group a serial of operation to a set. Input "BEgin" option, all the next operations become one part of this set until input "End" option. When "BEgin" option is active, input "undo begin" will end current set and begin a new one.
If inputting "undo begin" rather than "undo end", the "number" option will quit specified UNDO number and operations from beginning.
If users want to go back to operations before starting point, they must use "End" option (as the set is null). This could also be applied on U command. The mark made by "Mark" option will not display in UNDO group.
Mark, Back:
The "Mark" option places a mark in given up information. The "Back" option will give up all operations until marked one. If giving up one operation at one time, there will be a notice when the marked operation is to be given up.
If necessary, users could place any number of marks. Once use the "Back" option, it will return back to one mark and delete the mark. If the specified mark could not be found, the command prompt under the "Back" option:
This will undo everything. Ok? :
Input "Y", it will give up all operations.
Input "N", it will ignore this option.
If using "number" option to give up multiple operations, the UNDO command will stop at the marked one.