  We discuss the determination of the parameters of the pp and ppbar amplitudes
for the description of scattering in the Coulomb interference region. We put
enphasis on the possibility that the effective slope observed in the
differential cross section is formed by different exponential slopes in the
real and imaginary amplitudes (called B_R and B_I). For this purpose we develop
a more general treatment of the Coulomb phase. We analyse the differential
cross section data in the range from 19 to 1800 GeV with four parameters (sigma
, rho, B_I, B_R), and observe that we cannot obtain from the data a unique
determination of the parameters. We investigate correlations in pairs of the
four quantities, showing ranges leading to the smaller chi2 values. In the
specific case of p-pbar scattering at 541 GeV, we investigate the measurements
of event rate dN/dt at low |t| in terms of the Coulomb interference with
exponentially decreasing nuclear amplitudes. The analysis allows a
determination of the normalization factor connecting the event rate with the
absolute cross section.
