  The two-point functions of the energy-momentum tensor and the Noether current
are used to probe the O(3) nonlinear sigma model in an energy range below 10^4
in units of the mass gap $m$. We argue that the form factor approach, with the
form factor series trunctated at the 6-particle level, provides an almost exact
solution of the model in this energy range. The onset of the (2-loop)
perturbative regime is found to occur only at energies around $100m$.
