  Recently an idea for computing the entropy of black holes in the spin foam
formalism has been introduced. Particularly complete calculations for the three
dimensional euclidean BTZ black hole were done. The whole calculation is based
on observables living at the horizon of the black hole universe. Departing from
this idea of observables living at the horizon, we now go further and compute
the entropy of BTZ black hole in the spirit of statistical mechanics. We
compare both calculations and show that they are very interrelated and equally
valid. This latter behaviour is certainly due to the importance of the
observables.
