English: Original outlines in φ,ψ space proposed by G.N. Ramachandran in 1963. Solid lines enclose region allowed by hard-sphere bumps at standard radii; dashed lines show region allowed with reduced radii; dotted lines add region allowed when the tau angle (N-Calpha-C) is relaxed slightly. (Note that Ramachandran called the angles φ and φ', and that he put 0°,0° in the lower left corner rather than in the center as here - standard now since 1970.) Labels show the approximate location of common structural features such as α or 3-10 helix.