Crystallographic table 1

Indexing is normally carried out using an automated procedure (hence 'autoindexing') and gives the crystal orientation, an initial estimate of the unit cell dimensions with an idea of the crystallographic symmetry and an index for each reflection.
The unique reflection number is defined by the resolution of the diffraction data and the size of the unit cell; when combined with the number of amino acids and/or nucleotides that occupy the asymmetric unit, these values set the “observations-to-parameters” ratio for refinement of the model.