  In the context of a recently proposed method for computing exactly string
loop corrections regularized in the infra-red, we determine and calculate the
universal moduli-dependent part of the threshold corrections to the gauge
couplings for the symmetric $Z_2\times Z_2$ orbifold model. We show that these
corrections decrease the unification scale of the underlying effective field
theory. We also comment on the relation between this infra-red regularization
scheme and other proposed methods.
