  We calculate the black hole mass distribution function that follows from the
random emission of quanta by Hawking radiation and with this function we
calculate the black hole mass fluctuation. From a complete different
perspective we regard the black hole as quantum mechanical system with a
quantized event horizon area and transition probabilities among the various
energy levels and then calculate the mass dispersion. It turns out that there
is a perfect agreement between the statistical and the microscopic calculations
if and only if the area spectrum is linear. Accordingly, the quantum mechanical
properties of the black hole which are supposedly relevant only at Planckian
scales do leave an imprint in the black hole mass dispersion at much larger
scales where gravity can be dealt classically, as one would expect from the
correspondence principle.
