an oblique plane can not be seen in the three
principal projections.Figure 7.21 Oblique planes♦ Inclined plane: An inclined plane does not appear
true size in any of the principal projections. This form
of plane is seen as an edge in the profile view or in
the frontal view and foreshortened (distorted) in the
other two views
Figure 7.22. Inclined Planes