While the isotropic crystallite size and microstrain terms have no geometric implications, interpreting the anisotropic models from the numerical values is a challenge, particularly for the third form of each set. For this reason GSAS-II allows one to visualize the model for the average for the crystallite size and microstrain values in 3-D as a function of geometry. This is done in the GUI by selecting the plot type in the upper right as “Size” for crystallite size and “Mustrain” for microstrain. For the isotropic models a sphere is plotted, but for the uniaxial case it may be of some value to visualize the relative sizes of the on-axis vs. perpendicular broadening. For the ellipsoidal case, this is more useful as it shows both the lengths and orientation of the crystallite model. The plots for microstrain fitting from the generalized Stephens/Popa model can be unusual shapes where there is considerably more microstrain in directions diagonal to crystal axes, as opposed to along the crystal axes. Since overfitting, where too many terms are introduced, is a constant concern in Rietveld analysis, it is always worthwhile to look at this plot and consider if the values make sense with what is known about the material.