Actual W(r) for a test model constructed with the OPAL equation of state compared to that inferred from inversions using an EFF model as the reference model. The inversion results using 50 realizations of random errors from GONG and MDI mode sets are shown. The blue and green lines show the result for each of the 50 realizations for the GONG and MDI sets. Since the lines are close together, the result appears as one thick line in most places.