UCS defined by three points

A new UCS can be defined by means of three points that do not lie on the same line. Each of the points has a precisely specified meaning:

1st point	It defines the origin of the new co-ordinate system.
2nd point	It defines the direction of X-axis of the new co-ordinate system.
3rd point	It defines the side to which the Y-axis of the new co-ordinate system will point.

Note: Please read Rules for using a UCS.