  The onsets of toppling and dissipation in the BTW model are studied by
computer simulation. The distributions of these two onset times and their
dependences on the system size are also studied. Simple power law dependences
of these two times on the system size are observed and the exponents are
estimated. The fluctuation of the average (spatial) height in the subcritical
region is studied and observed to increase very rapidly near the SOC point.
