A priori estimates of errors in intensities for imperfectly spherical crystals

A priori estimates of errors in intensities for spheres arising from non-sphericity in crystal shape may now be readily determined from a recently published table of (1/A*)(∂A*/∂μR) values [Flack & Vincent (1978). Acta Cryst. A34, 489-491] using an expression given by Jeffery & Rose [Acta Cryst. (1964), 17, 343-350]. However, a new relationship between σ(R) and σ(r) is determined. The effects of crystal radius, non-sphericity and wavelength on intensity errors are discussed. The importance to the selection of crystals for electron density measurements is stressed. Universal curves of σ(r)/r, the error due to non-sphericity, against μr calculated for a range of intensity errors at θ = 0 and 45 ° are given.