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short communications
Owing to a printer's error, the equation given in the Discussion of the paper by Attfield, Cheetham, Cox & Sleight [J. Appl. Cryst. (1988). 21, 452–457] is incorrect. The correct equation is (Δρ/σ(Δρ)) = (1/P) |p2 − p1|/(σ21 + σ22)1/2.