= Crystallographic resolution
{title2=$d_{\min}$}
\b[Crystallographic resolution] describes the spatial detail represented by a diffraction data set and the resulting <electron density> map. In <X-ray crystallography>, its conventional numerical measure $d_{\min}$ is the smallest lattice-plane spacing represented by measured reflections. A smaller stated distance means finer nominal resolution.<Resolution in the IUCr Online Dictionary of Crystallography>[Definition: minimum plane spacing and measured diffraction range]{ref}
From <Bragg's law>, first-order diffraction at the largest measured glancing angle $\theta_{\max}$ gives
$$
d_{\min}=\frac{\lambda}{2\sin\theta_{\max}},
$$
where $\lambda$ is the <X-ray> <wavelength>. For an illustrative wavelength $1\,\mathrm{\mathring A}$ and $\theta_{\max}=30^\circ$, the nominal resolution is $1\,\mathrm{\mathring A}$. At the same wavelength and a maximum angle of15degrees, it is about $1.93\,\mathrm{\mathring A}$: collecting smaller-angle reflections alone omits finer spatial information.<Resolution in the IUCr Online Dictionary of Crystallography>[Definition and relation to Bragg's law]{ref}
The2000 structure of a bacterial <small ribosomal subunit> provides a concrete use of the term: its primary report describes refinement to3Å resolution and interprets <RNA>–<protein> architecture. That number characterizes the data/model's spatial detail, not an assertion that every atomic coordinate has exactly3Å uncertainty. Noise, missing reflections, directional coverage and model errors still matter.<Structure of the 30S ribosomal subunit by B. T. Wimberly and others>[Abstract: Thermus thermophilus30S subunit refined to3Å]{ref}
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