Description: This article describes a simple but powerful tool for use by valuation actuaries and auditors when evaluating current assumptions for use in GAAP net premium reserve methods that require retrospective updating for actual experience and assumption changes. As a supplement, this tool can fill some holes left by existing tools. It produces results that can be compared to materiality thresholds at any level of aggregation, from a single reserve cohort up to the combination of all cohorts for all products subject to retrospective net premium reserve requirements. It can also serve as a benchmarking tool for estimated the possible effects of an assumption change or to help in explaining the effects of an actual assumption change.