As has already been discussed, WCS is fixed, whereas UCS enables you to set your own coordinate system. For a certain view of the drawing, it is better to have the origin of measurements at some other point on or relative to your drawing objects. This makes locating the features and dimensioning the objects easier. The origin and orientation of a coordinate system can be redefined using the UCS command. The prompt sequence is as follows.
Current UCS name: *WORLD*
Enter an option [New/Move/OrthoGraphic/Prev/Restore/Save /Del/Apply/?/World] <World>: Select an option
This is the default option. ...