2. Data logging

2.1 Choice of crystal

The first and most important requirement is an excellent single crystal. It doesn't have to have perfect faces, although this is often a quality criterion. The ideal situation would be a sphere, a shape that eliminates the effects of absorption; however, this is not essential, as there are now excellent absorption correction methods that are transparent to the user, even if they are based on an empirical principle, such as the DIFABS calculation program.

It is absolutely essential that the sample is a single crystal, i.e. free from macles, the presence of which can often be detected by microscopic observation, which reveals re-entrant angles. In some cases, crystallization leads only to mottled crystals. To get around this difficulty, we...