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The computation of logic-stage delays is a fundamental sub-problem for many EDA tasks. Although accurate delays can be obtained via circuit simulation, we must estimate the input assignments that will maximize the delay. With conventional methods, it is not feasible to estimate the delay for all input assignments on large sub-networks, so previous approaches have relied on heuristics. We present a symbolic algorithm that enables efficient computation of the Elmore delay under all input assignments and delay refinement using circuit-simulation. We analyze the Elmore estimate with three metrics using data extracted from symbolic timing simulations of industrial circuits.