A hidden heat strip for providing heat at the edge of a roof to prevent formation of ice. A connection is established between the media switch and each of the participants in a given call or other communication. The device measuring the differential pressure is configured to be connected to a device for producing a fluid flow. to be achieved and maintained by adjusting the column pressure and aromatic reflux rate. The iterative execution process may include executing the first command on a computer and determining whether the computer performed a power management operation in response to the first command. If a first type of factor is detected as the factor in the power saving state, the power supply unit supplies power to the control unit and the image forming unit, and the control unit restricts the driving of the image forming unit.