This report deals with the value of flow calibration for decision making in sewer system studies. Primary data used in this investigation were the field measurement results from a prior infiltration/inflow study conducted for the Metropolitan District Commission (MDC), Boston, covering portions of West Roxbury-Newton-Brookline-Dedham in the Boston metropolitan area. The results are applicable for any sewer system flow measurement program. The present study included a variety of 'what if' scenarios for critical key manholes as to the amount of information available to develop stage/flow calibration curves. The findings indicate that the additional care and the costs involved in primary flow calibration of stage/flow curves for sewer system evaluations are well worth the effort, and, in many instances, could save the government valuable resources.