The watch is provided with a circular row of capacitive keys defined by transparent electrodes arranged on the inner face of the crystal of the watch and connected to a detection device via a multiplexer. A first and a second path are positioned downstream of the first processing tray in a direction of sheet conveyance and configured to convey a first and a second sheet stack, respectively. Differential measurements between the two cavities occur simultaneously, which reduces errors due to cavity drift. The formulations are capable of being uniformly delivered from drug delivery systems at an exit shear rate of between about 1 to 1\xd710\u22127 reciprocal second.