# Tidying the Structure

1. The key numbers to look at are $R_{1}$, $wR_{2}$, max and min Q peak values (also called highest peak and deepest hole), Goof, Hooft and Flack which you should examine after each refinement.
• The values of $R_{1}$ and $wR_{2}$ are an indication of the agreement between Fc and Fo and should decrease as the refinement proceeds. Very high values of R1/wR2 (e.g. > 40/70 respectively) suggest that the structure solution is incorrect.
• Hooft $y$ and Flack $x$ are applicable only to structures in non-centrosymmetric space groups (i.e. not containing an inversion centre). They are displayed with an error and should be close to zero if the structure solution is correct, while ~1 implies the structure should be inverted and values significantly different from 0 or 1 indicate a racemic twin.
3. Go to the tab and open the header tab if there are one or two reflections that have very large $|F_{calc}^{2}-F_{obs}^{2}|/esd$. These values they may need to be omitted. Such reflections are evident as their values are significantly out of line with the rest of the reflections. If it seems necessary to omit more than a handful of reflections, there is probably a reason that reason should be carefully investigated.