Owing to a printer's error, the fourth equation given in the Abstract of the paper by Åsbrink, Kihlborg & Malinowski [J. Appl. Cryst. (1988). 21, 960–962] is incorrect. The correct equation is {\bar \beta}_c(0–7.41 GPa) = −3.35 × 10−4 (GPa)−1.