Abstract
Single-crystal diffractometers derived from inclination Weissenberg goniometers can be adapted to measure more than one reflection at a time. Two reflections can be measured simultaneously, one from each of any two levels that are symmetrically on either side of the flat-cone setting, or several reflections can be measured quasi-simultaneously, one from each level within about ±0.05 r.l.u. of the flat-cone setting. The modifications which permit these new modes of operation are described, together with corresponding changes in the design and use of four-circle diffractometers. The general relationships between the two types of diffractometer are also discussed.