TheXABS2 Fortran program calculates an empirical absorption correction based on minimization of the 2 differences betweenF2obsandF2calc. The basic algorithm has been used in the crystallography laboratory at the University of California, Davis for over a decade, in the form of the programXABS. XABSrelied upon an approximately linear relationship for spherical crystals between the transmission factor and sin2θforθ≃ 30° whenμR≃ 5. InXABS2, deviations from linearity are accounted for by a cubic equation in sin2θ, which makes it applicable over the whole range of diffraction angle. The program needs no data in addition to the unique set but assumes a bisecting (symmetric) data‐collection mode on a four‐circle diffractometer. Since it does not require knowledge of the diffractometer setting angles, it can be applied even in cases where details of the original data collection