  It is shown that the fluctuations of the jamming coverage upon Random
Sequential Adsorption ($\sigma_{\theta_J}$), decay with the lattice size
according to the power-law $\sigma_{\theta_J} \propto L^{-1 / \nu_J}$, with
$\nu_{J} = 2 / (2D - d_f)$, where $D$ is the dimension of the substrate and
$d_{\rm f}$ is the fractal dimension of the set of sites belonging to the
substrate where the RSA process actually takes place. This result is in
excellent agreement with the figure recently reported by Vandewalle {\it et al}
({\it Eur. Phys. J.} B. {\bf 14}, 407 (2000)), namely $\nu_J = 1.0 (1)$ for the
RSA of needles with $D = 2$ and $d_f = 2$, that gives $\nu_J = 1$. Furthermore,
our prediction is in excellent agreement with different previous numerical
results. The derived relationships are also confirmed by means of extensive
numerical simulations applied to the RSA of dimers on both stochastic and
deterministic fractal substrates.
