We study an equivalent definition of the Hausdorff-Besicovitch dimension in terms of a system Φ(Q ∞ ) of cylinders of the Q ∞ -expansion. Sufficient conditions for the system Φ(Q ∞ ) to be faithful for the evaluation of the Hausdorff-Besicovitch dimension in the unit interval are found; fine fractal properties of probability measures with independent Q ∞ -digits are investigated (we do not assume that the Q ∞digits are identically distributed). k s=1 q i s 2010 Mathematics Subject Classification. Primary 60G30, 11K55, 28A80. Key words and phrases. Q ∞ -expansions, faithful systems of coverings, singularly continuous probability distributions, Hausdorff-Besicovitch dimension of a set, Hausdorff dimension of a measure. The first author was supported by the Project DFG 436113/97. The second author was supported by the Projects DFG 436 UKR 113/97 and DFG KO 1989/6-1 and the Alexander von Humboldt Foundation.