2012

When an operation cannot be undone, the command name is displayed but
no action is performed. Operations external to the current drawing, such as
plotting or writing to a file, cannot be undone.
If you changed modes or used transparent commands during a command,
their effects are undone, along with the effects of the main command.
The U command is equivalent to entering undo 1.
UCS
Quick Reference
See also:
■ Work with the User Coordinate System (UCS)
■ UCSSELECTMODE
Sets the origin and orientation of the current UCS.
Access Methods
Button
NOTE By default, the Coordinates panel is hidden in the Drafting & Annotation
workspace. To display the Coordinates panel, click the View tab, then right-click
and choose Show Panels, and then click Coordinates. In 3D workspaces, the
Coordinates panel is on the Home tab.
Ribbon: View tab ➤ Coordinates panel ➤ UCS
Menu: Tools ➤ New UCS
Toolbar: UCS
Shortcut menu: Right-click the UCS icon and click an option.
Summary
The UCS is the active coordinate system that establishes the XY plane (work
plane) and Z-axis direction for drawing and modeling. Control the UCS origin
1966 | Chapter 21 U Commands