For the single residue models of and the chi-squared value χ2i which is optimised is simply Equation (15.13) on page in which the relaxation data is that of residue i. However for the global models and in which all selected residues are involved the optimised chi-squared value is the sum of those for each residue,
|χ2 = χ2i,||(15.8)|
where i is the residue index and l is the total number of residues used in the analysis. This is equivalent to Equation (15.13) when the index i ranges over the relaxation data of all selected residues.