  This work studies universal finite size scaling functions for the number of
1d spanning avalanches in a two-dimensional disordered system with boundary
conditions of different nature and different aspect ratios. For this purpose,
we consider the 2d Random Field Ising Model at T = 0 driven by the external
field H with athermal dynamics implemented with periodic and forced boundary
conditions. We choose a convenient scaling variable z that accounts for the
deformation of the distance to the critical point caused by the aspect ratio.
Moreover, assuming that the dependence of the finite size scaling functions on
the aspect ratio can be accounted by an additional multiplicative factor, we
have been able to collapse data for different system sizes, different aspect
ratios and different nature of the boundary conditions into a single scaling
function Q.
