  The dips observed in the differential cross sections of elastic pp and
p$\bar{\rm p}$ scattering are studied in terms of the locations of the zeros of
the real and imaginary parts of the amplitude and of the sign of real part at
large $|t|$. It is confirmed that the differences in shapes of the dips in the
pp and p$\bar{\rm p}$ systems are determined by a change of sign of the real
tail, which seems to be determined by perturbative QCD contributions.
