or as a backup source when the facility failed. Unlike in the public telephone network, which has a standard ringing cadence (the repeating pattern of ringing and silence), the ringing cadence when using a magneto depended on the skill of the operator. When ringing local extensions, some switchboard operators used local codes of ringing to indicate internal, external or urgent calls. Linesman's test sets also included a magneto, for use when ringing out to either the exchange or the subscriber, from anywhere along the line. Their use extended into the 1980s. See also Magneto Ringer box References Electrical generators History of the telephone