Having established the state of stress at $H$, the principal stresses can now be computed using either the plane stress transformation equations or the Mohr's circle transformation.

For this example, we will use Mohr's circle. We first plot two points: the state of stress on the $x$ face and the state of stress on the $y$ face. From these two points, the circle, which represents combinations of $\sigma$ and $\tau$ at all possible orientations, can be constructed.

For this case, the center of the circle is $C=-9.20 MPa$ and the radius is $R=10.24 MPa$.