Electronic and mechanical sources of error in diffractometry

The possible sources of error which arise from mechanical and electronic design features are discussed. The need for self-checking procedure for off-line operation and the advisability of an automatic restart procedure after fortuitous stoppage is stressed. Various features of mechanical design are dealt with in relation to physical stability. In particular, the need for careful expert alignment procedures is pointed out. It is suggested that this aspect rightly belongs in the hands of the manufacturer rather than of the user. Comments on the essential features in the design of goniometer heads are given and the design for a special `orientation inverter' head particularly suitable for quarter-circle Eulerian cradle diffractometers is described.