Abstract: A method of silent monitoring in a telephone system by a monitor comprising storing in a first table in a memory, correspondence between an agent identifier and a telephone set directory number used by the agent, requesting silent monitoring of the agent using the identifier, checking the table to determine the directory number of the telephone set corresponding to the agent, creating and storing a record containing the directory number, an identifier of the monitor and the agent identifier, in the event a telephone call is in process using the telephone set, conferencing a telephone set used by the monitor with the telephone set used by the agent, using a one way audio path toward the telephone set used by the monitor, in the event the telephone call in process clears, maintaining the record until the telephone set used by the monitor has gone on-hook, and continuing to monitor subsequent calls involving the telephone set used by the agent prior to the telephone set used by the monitor going on-hook, maintai

Abstract: For detecting changes of level of a moving surface, a sharply defined light pattern is directed on to the surface and an image of the pattern is formed on a multiple photodiode strip so that a predetermined point of reference of the image is variably located on the strip depending on variation in level of the surface, the photodiode strip is repetitively scanned to create a voltage waveform repetitively defining the variable position of the point of reference on the image in relation to the fixed position of a point of reference on the photodiode strip, and the waveform is analysed to determine the variations in level of the moving surface.