The recorded series of two-dimensional diffraction patterns, each corresponding to a different crystal orientation, is converted into a three-dimensional model of the electron density; the conversion uses the mathematical technique of Fourier transforms, which is explained below. Each spot corresponds to a different type of variation in the electron density; the crystallographer must determine "which" variation corresponds to "which" spot ("indexing"), the relative strengths of the spots in different images ("merging and scaling") and how the variations should be combined to yield the total electron density ("phasing").