A developing unit includes a developer containing unit that contains developer, a developer carrier that has a moving surface, and carries the developer, a magnetic force generator that attracts the developer onto the moving surface by a magnetic force generated from a plurality of magnets, and a restricting member that restricts a layer thickness of the developer. A sump cavity is provided in fluid communication with the first zone and a sump vent. A second motorgenerator is continuously connected for common rotation with the input member. The invention provides routine, automated, continuous, and real-time monitoring for patients undergoing IV therapy.