PLANE allows you to define the desired construction plane.
This option is also assigned an Immediate Mode command.

Define a new construction plane by choosing from the
following options:

3 PTS - to indicate three points on the screen. The
positive direction for the x axis passes from the first
point to the second point. The position of the third point
relative to the other two points determines the direction
of the y axis (and consequently the z axis).

PT/LINE- to select a point (or position) in space and the
two endpoints of a selected line entity.

2 LINES - to select the endpoints of two lines, and the 
3-D intersection (or potential 3-D intersection) of the 
lines.

VPORT - to assign the plane associated with a particular
viewport's view.

ENTITY - to  define a plane by selecting an existing 
planar arc, conic, or 2-D spline entity.

KEY-IN - to define a plane by assigning a concatenated
series of rotations.

CP = DV - to automatically set the construction plane to 
the display view assignments.

SAVE - to store the defined construction plane in the
database. The next available number in the database is
assigned to this new plane.
