The initial stages of the growth of a tin film on a clean niobium substrate have been studied. The tin was evaporated slowly and the Anger signals of both the substrate and the tin overlayer were monitored as a function of the exposure time. The experimental results have been plotted as an AA-t plot for comparison with theoretical models of the different possible modes of the growth of films. The plot was also used to determine the attenuation length of the Sn and Nb Anger electrons.