  A crucial issue in cosmology is the determination of the fluctuation power
spectrum.The standard picture of the matter clustering, the Cold Dark Matter
model (and its variant), assumes that,on scales smaller than a certain
``flattening scale'' $\lambda_f$, the power spectrum increases with the scale,
while on much larger scales it decreases so to match the tiny fluctuations
observed in the microwave background. The standard picture also assumes that,
once a statistically homogeneous sample is reached, the power spectrum
amplitude is fixed, and any major variation should be attributed to luminosity
segregation. However, the determination of $\lambda_f$ and of the absolute
amplitude, if any, is still matter of debate. In particular, there is no
consensus on whether the turnaround has been detected or not, and on the actual
importance of the luminosity segregation effect. We show that, due to the
finiteness of the sample the standard analysis of self-similar (fractal)
distributions yields a turnaround for scales close to the survey scale, and a
systematic amplitude shift with the survey scale. We point out that both
features, bending and scaling, are in agreement with recent determination of
the power spectrum, in particular with the CfA2 spectrum. We remark that the
standard power spectrum is not a well defined statistical tool to characterize
the galaxy distribution when a homogeneity scale has not been reached. In order
to perform an analysis that does not imply any a priori assumption one should
study the PS of the density, rather than the PS of the density contrast.
