The Chi1-Chi2 plots show the chi1-chi2 sidechain torsion angle combinations for all residue types whose sidechains are long enough to have both these angles.
The shading on each plot indicates how favourable each region on the plot is; the darker the shade the more favourable the region. The data on which the shading is based has come from a data set of 163 non-homologous, high-resolution protein chains chosen from structures solved by X-ray crystallography to a resolution of 2.0Å or better and an R-factor no greater than 20%.
The numbers in brackets, following each residue name, show the total number of data points on that graph. The red numbers above the data points are the reside-numbers of the residues in question (ie showing those residues lying in unfavourable regions of the plot).
The main options for the plot are:-
These options can be altered by editing the parameter file, procheck.prm, as described here.