  We show how the renormalized force correlator Delta(u), the function computed
in the functional RG (FRG) field theory, can be measured directly in numerics
and experiments on the dynamics of elastic manifolds in presence of pinning
disorder. For equilibrium dynamics we recover the relation obtained recently in
the statics between Delta(u) and a physical observable. Its extension to
depinning reveals interesting relations to stick-slip models of avalanches used
in dry friction and earthquake dynamics. The particle limit (d=0) is solved for
illustration: Delta(u) exhibits a cusp and differs from the statics. We propose
that the FRG functions be measured in wetting and magnetic interfaces
experiments.
