Breddin in 1958 devised a graph based on angular shear strainj, the principal strain ratio R and the angle q' that the deformed line makes with principal extension direction and the original angle q. The relationship is given by (Ramsay 1967):
And R =tanq'/tan(90-q)
Place your left mouse button clicked in the area covered by red curves of R-1 and see the values returned in the fields that will appear only on Mouse Down action.
The above is the footnote for this simple demo on Breddin graph whose screenshot is shown.