  In the framework of the impact picture we compute the analyzing power $A_N$
for $pp$ elastic scattering at high energy and in the very forward direction.
We consider the full set of Coulomb amplitudes and show that the interference
between the hadronic non-flip amplitude and the single-flip Coulomb amplitude
is sufficient to obtain a good agreement with the present experimental data.
This leads us to conclude that the single-flip hadronic amplitude is small in
this low momentum transfer region and it strongly suggests that this process
can be used as an absolute polarimeter at the BNL-RHIC $pp$ collider.
