Scaling and postrefinement of intensity data

The goal of data collection is a set of consistently measured, indexed intensities for as many of the reflections as possible. After data collection, the raw intensities must be processed to improve their consistency and to maximize the number of measurements that are sufficiently accurate to be used. 

A complete set of measured intensities often includes distinct blocks of data obtained from several (or many) crystals and, if data are collected on film, from many films. Because of variability in the diffracting power of crystals, the intensity of the X-ray beam, and the sensitivity of films (if used), the crys-tallographer cannot assume that the absolute intensities are consistent from one block of data to the next. An obvious way to obtain this consistency is to compare reflections of the same index that were measured from more than one crystal or on more than one film and to rescale the intensities of the two blocks of data so that identical reflections are given identical intensities. This 

Data from partial reflections can be interpreted accurately through postrefinement of the intensity data. This process produces an estimate of the partiality of each reflection. Partiality is a fraction p (0 p 1) that can be used as a correction factor to convert the measured intensity of a partial refection to an estimate of that reflection s full intensity. 

Scaling and postrefinement are the final stages in producing a list of internally consistent intensities for most of the available reflections. 

The unit-cell dimensions determine the reciprocal-lattice dimensions, which in turn tell us where we must look for the data. Methods like oscillation photography require that we know precisely which reflections will fall completely and partially within a given oscillation angle so that we can collect as many reflections as possible without overlap. So we need the unit-cell dimensions in order to devise a strategy of data collection that will give us as many identifiable (by index), measurable reflections as possible. 

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