The equiv program allows for the analysis and management of data collections from X-ray single crystal diffractometry (namely, a generally large set of hkl indices, together with the corresponding diffraction intensities, or structure factors, and standard deviations). It is particularly useful for high symmetry systems, where a checking of the intensities of the equivalent reflections (star) is a good way of estimating the quality of the data collected and of the goodness of the anisotropic absorption correction. The program proceeds by:

- grouping together equivalent reflections, according to the Laue or point group specified in input;

- calculates averages and standard deviations over the equivalents;

- marks "anomalous reflections" (those with intensity too low with respect to the maximum one in the star, or those whose intensity differs from the average one more than a certain threshold given in input);

- allows optionally the elimination from the input data set of such anomalous reflections, according to different criteria as will be outlined below;

- creates new files in which the original standard deviations (generally based on counting statistic) are replaced by standard deviations on equivalents.

Moreover the program allows for the selection of particular classes of reflections (e.g. those forbidden by the presence of screw axes, glide planes and cell centering) specifying selection rules in a user-writable routine (and recompiling the program; actually several selection rules are already implemented and can be used as a template for writing new ones). Other facilities offered by equiv are  illustrated in the Keywords section (see, in particular, the detailed description of each instruction).