For Relative Gas Diffusivity, the two solvers EJ and LIR are available and can be chosen from the pull-down menu. The solver settings are similar to those available in the DiffuDict module, so please refer to the description in the DiffuDict handbook for details. Note, that in DiffuDict more options are available, that cannot be selected in the Relative Diffusivity options dialog (e.g. no restart options are available here).