AutoCAD 2008 User's Guide > Create and Modify Objects > Use Precision Tools > Use Coordinates and Coordinate Systems (UCS) > Specify Workplanes in 3D (UCS) > Understand the User Coordinate System in 3D > 
Understand the User Coordinate System in 3D
Concept Procedure Quick Reference
 
 
 

To enter coordinates relative to the WCS

To specify a new UCS with three points

To rotate the UCS around a major axis