A retention assembly includes a platform, a bracket, and a resisting member rotatably connected to the platform. According to the invention, clusters are organized into hierarchical tree arrangements, with addresses assigned in a manner that facilitates routing messages. An oil delivery system is coupled to the selector switch for selecting one of varying amounts of oil to be delivered to the kettle in conjunction with selecting the rate or amount of heat to be delivered to the kettle. The height of the first channel is greater than the height of the more distal second channel.