International
Tables for Crystallography Volume C Mathematical, physical and chemical tables Edited by E. Prince © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. C, ch. 9.4, p. 778

By means of the retrieval system CRYSTIN (Sievers & Hundt, 1987), sets of structures were selected and combined; these contained:

For the M structures so defined, n interatomic distances were calculated for the atoms and ions in question. In so doing, all symmetrically equivalent and nonequivalent distances were taken into account. From these, a frequency distribution was calculated automatically. All distances d were collected into ranges of 2 pm. In (9.4.2.1)–(9.4.2.2), n(d) is the number of distances in the range with midpoint d, is the midpoint of the lowest range, and is the midpoint of the highest range selected for the calculation of the mean. The choice of and is discussed in Section 9.4.3. The mean and the standard uncertainty (s.u.) of one set of distances were calculated by means of the equations
References
Sievers, R. & Hundt, R. (1987). Crystallographic information system CRYSTIN. In Crystallographic databases, edited by F. H. Allen, G. Bergerhoff & R. Sievers, pp. 210–221. Bonn/Cambridge/Chester: International Union of Crystallography.