Atomic form factor patterns are often represented as a function of the magnitude of the "scattering vector" formula_13. Here formula_14 is the angle between the incident x-ray beam and the detector measuring the scattered intensity, and formula_15 is the wavelength of the X-rays. One interpretation of the scattering vector is that it is the "resolution" or "yardstick" with which the sample is observed. In the range of scattering vectors between formula_16 Å−1, the atomic form factor is well approximated by a sum of Gaussians of the form