  We use the replica variational method to study the effects of weak point
disorder on the variance of the internal field distribution measured in NMR and
muon-spin rotation experiments in type-II superconductors. We show that for a
simple model there is significant magnetic field dependence which is extrinsic
and disorder-driven, and does not have a microscopic (non $s-$wave pairing)
origin. Results are presented where we examine the dependence of the magnetic
field variance upon the strength of the applied external field.
