“…When ⟨ n ⟩ is computed over long times, λ is a constant. However, as the observation or averaging time becomes shorter, the observed rate of formation will deviate from the mean due to random variations in the time interval between successive events, or equivalently, random variations in the number of events within the defined time interval . This behavior, which is illustrated in Figure , can be described by considering the variance in the observed event rate, n /τ, around the mean, given by …”