This diffractometer used a beam from the hot source to maximise the Q range of measurements to determine partial strucure factors aided by isotopic substition. Great stability was demanded of these measurements to enable the small differences due to the different isotopes employed, and differences between the sets of measurements yields the structural information (Chieux). Although pulsed source instruments could cover a greater Q range the analysis and simpler corrections required by the monochromatic source data yielded results of equivalent value.

When IN1 was rebuilt it was decided to incorporate D4 as a component using the IN1 monochromator, and time-share use of the hot source beam. New multi-detectors were introduced to speed up data collection during the reduced time available..