  The role of the operator-product expansion in QCD calculations is discussed.
Approximating the two-point correlation function by several terms and assuming
an upper bound on the truncation error along the euclidean ray, we consider two
model situations to examine how the bound develops with increasing deflection
from the euclidean ray towards the cut. We obtain explicit bounds on the
truncation error and show how they worsen with the increasing deflection. The
result does not support the believe that the remainder is constant for all
angles in the complex energy plane. Further refinements of the formalism are
dicussed.
