Principal planes are always orthogonal.

Planes of maximum shear stress are always at 45° to principal planes.

The stress analysis performed in Cartesian coordinate and in polar coordinates will result in different principal stresses at a point.

The sum of the normal stresses at a point in an orthogonal coordinate system is independent of the orientation of the coordinate system.

In plane strain there are three principal stresses and in plane stress there are two principal stresses.

The in-plane maximum shear stress and the maximum shear stress are the same for a point in plane stress if principal stresses 1 and 2 are both compressive.

The in-plane maximum shear stress and the maximum shear stress are the same for a point in plane stress if principal stresses 1 and 2 are both tensile

The in-plane maximum shear stress and the maximum shear stress are the same for a point in plane stress if principal stress 1 is tensile and principal stress 2 is compressive.

Two planes passing through a point can be represented by the same point on Mohr’s circle.

Two points on Mohr’s circle can represent the same plane.