One of the most efficient non-destructive techniques for finding hidden faults in a plate is the use of ultrasonic Lamb waves. These waves are reflected by faults, and from this reflection, we can locate the faults. For that, we need to know how the Lamb waves propagate. Their propagation is determined by the dynamic elastic constants C_pq, so we must find these constants. These constants cannot be measured directly; instead, we measure the dependence of the speed of frequency c(f), and we must reconstruct C_pq from the measured values of c(f). In this paper, we show how this can be done in the presence of probabilistic, interval, and fuzzy uncertainty.