Perturbation theory is a collection of methods for determining the effect of a known perturbation on a given physical system. Inverse perturbation theory is defined as a collection of methods for determining the nature of the perturbation itself. This Note presents one method related to inverse perturbation theory, where calculated and measured parameters in one system bound the expected measured parameters in a related system subject to the same uncertainties as in the first system. The method is applied to reactor theory problems.