Residuals after subtracting the best-fit exponential model from the cumulative distribution function of the waiting times δt between one avalanche and the next. The errors are calculated using Poisson statistics. From left to right, we show setups 1, 2, and 3. The residuals for setup 3 are quite large, indicating that in this case, the distribution function of δt is more complex than an exponential law. This indicates a correlated process.