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The problem of determining the crystal thickness at which the kinematical theory can be used in electron diffraction is discussed by calculating distribution functions over the number of scattering events from the N beam dynamical theory. We consider coronene (C24H12) as representing a model for a biological crystal having a rather large unit cell and a large number of excited beams in the Laue case. For a thick crystal a symmetrical Poisson distribution is obtained, and this leads to a mean free path for elastic scattering of 83 Å for coronene at 100 kV. In the limiting case of one unit-cell dimension of thickness at 100 kV, it is found that the kinematical theory should be a good approximation, the multiple scattering error being 5%. The possibility of decreasing multiple elastic scattering errors by raising the accelerating voltage is considered, and when Fujiwara's relativistic corrections are taken into account the improvement above 500 kV is predicted to be negligible.