A vacuum cleaner has an adjustable-height suction nozzle. A diaphragm switch is mounted in the housing inside the nozzle and determines a differential air pressure of the operating vacuum cleaner. Voltage source terminals are self-energizing with the rotation of a rotatable brush inside the nozzle and an indicator lamp is illuminated, or extinguished, upon developing a proper suction as establised by the proper adjusted height of the nozzle relative to the floor surface. The foregoing abstract is merely a resume of one general application, is not a complete discussion of all principles of operation or applications, and is not to be construed as a limitation on the scope of the claimed subject matter.