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*PROCHECK-NMR - Sample plots*

# 3. Chi1-Chi2 plots

## Description

The Chi1-Chi2 plots show the **chi1-chi2** torsion angle combinations
for all residue types that 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 **numbers within each data
point** correspond to the **model number**, while any **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).

## Options

The main options for the Chi1-Chi2 plots are:-

- The cut-off
*G*-factor defining which points are to be labelled
as lying in unfavourable regions of the plot.
- The plot can be in colour or black-and-white.

These options can be altered by editing the parameter file,
**procheck_nmr.prm**, as described here.

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*PROCHECK-NMR - Sample plots*