AbstractA criticism sometimes made of dynamic programming is that in deterministic problems, optimal decisions are calculated which are never needed, as the decisions relate to states which never arise. In this paper we describe how some of these "redundant" calculations have been used, in a certain problem, to derive a working rule of general validity.The problem concerns the installation and replacement of an item of electrical equipment at a large number of sites, to meet a known load at each site which increases exponentially at a known rate.