By Plane allows the creation of a UCS by assigning a plane either X or Y axis, without the assigning of a coordinate like By Pick in the workflow above.
Name the UCS.
Select UCS creation method By Plane.
Optionally, fence area to constrain plane creation.
Use the fence tool to highlight an area for plane creation.
Select X or Y direction to be assigned to the plane.
Double click the surface to region grow a plane.
Single click plane again to set the positive X or Y direction as shown by an arrow.
Click Create to finish and create a UCS.