The various approximations that were used to deduce solute concentration from the Whipple equation were considered. These included those which were intended to permit the determination of grain boundary diffusivities from experimental data. An algorithm was proposed which avoided these approximations. It was shown that the algorithm was stable against moderate experimental error and, unlike the alternatives, could be used to minimize the effect of such errors.

J.W.Evans: Journal of Applied Physics, 1997, 82[2], 628-34