  Frequency analysis of long-term ultra-precise photometry can lead to precise
values of rotation frequencies of rotating stars with ``hump and spike''
features in their periodograms. Using these features, we computed the rotation
frequencies and amplitudes. The corresponding equatorial rotational velocity
($v_{\rm rot}$) and spot size were estimated. On fitting the autocorrelation
functions of the light-curves with the appropriate model, we determined the
starspot decay-time scale. The $v_{\rm rot}$ agrees well with the projected
rotational velocity ($v\,{\rm sin}\,i$) in the literature. Considering a single
circular and black spot we estimate its radius from the amplitude of the
``spike''. No evidence for a significant difference in the average ``spike''
amplitude and spot radius was found for Am/Fm and normal A stars. Indeed, we
derived an average value of $\rm \sim 21\pm2$ and $\sim 19\pm2\,{\rm ppm}$ for
the photometric amplitude and of $\rm 1.01\,\pm\,0.13$ and
$1.16\,\pm\,0.12\,R_{\rm E}$ for the spot radius (where $R_{\rm E}$ is the
Earth radius), respectively. We do find a significant difference for the
average spot decay-time scale, which amounts to $3.6\pm0.2$ and $1.5\pm0.2$
days for Am/Fm and normal A stars, respectively. In general, spots on normal A
stars are similar in size to those on Am/Fm stars, and both are weaker than
previously estimated. The existence of the ``spikes'' in the frequency spectra
may not be strongly dependent on the appearance of starspots on the stellar
surface. In comparison with G, K and M stars, spots in normal A and Am/Fm stars
are weak which may indicate the presence of a weak magnetic field.
