For the single residue models of
and
the chi-squared value *χ*^{2}_{i} 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,

χ^{2} = χ^{2}_{i}, |
(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.

The relax user manual (PDF), created 2019-03-08.