Highlighting the Non-Included Angle

Use the include angle highlighting tool to show the non-included angle between flat mesh triangles.

On the 3D View contextual tabs set, on the Mesh tab, in the Tools group, for the  Include angle icon, specify the non-included angle and click the icon.
The non-included angle is highlighted in the 3D view with pink color where applicable.

Figure 1. Example of non-included angle displayed in POSTFEKO.