The variability in coating, namely the distribution of coating mass on the population of particles comprising the batch, has been studied by Mann [11] and Cheng and Turton [12] and [13]. Both the cycle time distribution and the coating per particle per pass distribution affect the overall uniformity of the batch. For fluid beds without significant dead zones, the major causes of coating variability are due to (i) the variability in the amount of coating material particles receive per pass through the spray zone, and (ii) the overall coating time. When scaling up coating processes, the variance of the coating per pass distribution tends to increase but this effect is counterbalanced by the longer coating times that decrease the coating variability.