Relative b co-ordinate - methods involving single h/a derivatives (Book X). Index and summaries at front. Includes collaborators' work. Divider card 23.6 "Theory" includes notes by H. Wyckoff (a principal collaborator in this work) and F.H.C. Crick. Calculations, structure factors, printouts, charts, phase circles, graphs, contour maps. Few pages dated, June-November 1956.