2011

If you specify a third point, the UCS rotates around the X axis such that the
positive Y half of the XY plane of the UCS contains the point.
The three points specify an origin point, a point on the positive X axis, and a
point on the positive XY plane.
NOTE If you enter the coordinates for a point and you do not specify a Z
coordinate value, the current Z value is used.
Face
Aligns the user coordinate system to a face on a 3D solid.
Select a face by clicking within the boundary or on an edge of the face. The
UCS X axis is aligned with the closest edge of the original face selected.
Next Locates the UCS on either the adjacent face or the back face of the
selected edge.
Xflip Rotates the UCS 180 degrees around the X axis.
Yflip Rotates the UCS 180 degrees around the Y axis.
Accept If you press Enter, accepts the location. The prompt repeats until you
accept a location.
Named
Save and restore commonly used UCS orientations by name.
UCS | 1975