The chemical shift index is a method for predicting protein secondary structures from the observed chemical shifts of the protein backbone and CB atoms. In general, if a run of negative values is present in the consensus plot a helix is predicted for this region of the protein. If a run of positive values is present a beta strand is predicted.
The plots shown are generated according to the algorithm of Wishart and coworkers using the standard chemical shift values reported in their publications (see http://www.bmrb.wisc.edu/ref_info/csishift.txt).
See the references below for details.