The book gave a formula CU = RK, where CU is O(U) of C in the sense of big O notation, R is the instantaneous rate at which those error reports would occur under steady traffic, and K is the e-folding time of the rollout.
As the exponential rollout progresses, if a lower magnitude of increase in C results in a higher order of magnitude of increase in RK, your estimate of U should be higher than 1. In practice, you should calculate the increase from the moment you start the rollout and compare ratios, not order of magnitudes, between C and RK. That is, calculate U from RK / C.