A droplet actuator comprising a substrate comprising an electrode coupled to a voltage source, wherein the droplet actuator is configured such that when voltage is applied to the electrode, an electrostatic energy gradient is established at a surface of the substrate which causes a droplet to be transported in a direction established by the energy gradient. The path includes at least one link between the subscriber node and the publisher node, and the recordation involves recording each distinct link in the path between the subscriber node and the publisher node. A raised cylinder extends upwards from the interior floor surface. The CMD signals are input to a CMD circuit that operates in conjunction with a Dual Port Router to execute the at-speed operations of a circuit. The hauling bar is arranged in one of the plurality of sheaths. The incentive may be provided via a credit to the payment account, or as an online virtual reward on a social networking or gaming website.