  The scaling properties at low $x$ of the proton DIS cross section and its
charm component are analyzed with the help of the quality factor method.
Scaling properties are tested both in the deep inelastic scattering data and in
the structure functions reconstructed from CTEQ, MRST and GRV parametrisations
of parton density functions. The results for DIS cross sections are fully
compatible between data and parametrisations. Even with larger error bars, the
charm component data favors the same geometric scaling properties as the ones
of inclusive DIS. This is not the case for all parametrisations of the charm
component.
