Actually when the Fourier transform of an EM is indexed and diffraction intensities and phases are measured, the corresponding EM is averaged according to the lattice periodicity. Here the averaging is done further according to the space group symmetry by forcing both the amplitude and phase of structure factors to obey the symmetry relationships*. The calculation is first carried out in reciprocal space. Make the sub window containing the reciprocal image (top right of the figure below) the current window. Click the 'Sym. average' button  . A dialog box (upper left) will ask the user to specify the plane group. Or, as an alternative the user can put in a space group symbol. However the projection of the given space group should match one of the plane groups listed in the dialog box. A residual map (lower left) will then appear with a green "+" mark at the position of minimum residual. If necessary (but not recommended), the user can adjust the position of the mark. By clicking OK, the averaged reciprocal image (bottom right) will be calculated according to the position of the "+" mark.

Fourier transforming the averaged reciprocal image (upper-left corner of the next figure), we get the average image in real space (middle). The latter can be zoomed by clicking the 'Zoom' button . Be sure to adjust also the 'Width' and 'Height' in the dialog box appropriately. The green lines on the enlarged image (right sub window) are unit cell borders which can be shown or hid using the corresponding function in the pull-down menu "Image".