Finite strain is strain that is more than a few per cent.
At right is the Mohr Circle corresponding to the ellipse. Shear is a bit more complicated when dealing with finite strain. The change in angle C is a measure of shear. Writing it this way allows us to see that the geometrical relationship at left must hold. Mohr Circle constructions for finite strain aren't used very much to calculate dimensions or shear since it's usually just as easy, and more clear, to work directly from the ellipse.