  We establish both experimentally and theoretically the relation between off
the edge and internal avalanches in a sandpile model, a central issue in the
interpretation of most experiments in these systems. In BTW simulations and
also in the experiments the size distributions of internal avalanches show
power laws and critical exponents related with the dimension of the system. We
show that, in a SOC scenario, the distributions of off the edge avalanches do
not show power laws but follow scaling relations with critical exponents
different from their analogous for the internal avalanche distributions.
