The avalanche-size exponent, τ, and the avalanche-dimension, D, for regular lattice structures with coordination numbers, K = 2, 4, 6, 8 and circumference C, see Fig 3(a) for the data collapse.

The scaling relation D(2 − τ) = 1 is fulfilled and, within error bars, both scaling exponents (apart from K = 8 and C = 2000) are consistent with the universality class of the two-dimensional directed sandpile model τ = 4/3 and D = 3/2. The numerical result for K = 8, C = 2000 and 4000 suggests that the apparent drift is due to finite size effects.