Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems (1921)
Smith, Arthur Bessey, b. 1875, Campbell, Wilson Lee · New York : McGraw-Hill · leaf 87
there is a free trunk in the first level of the group, the rotary actionstarts at once. If all levels are busy, the switch will rotate on the upper level of thegroup anyway, because the corresponding vertical-bank contact is open.Since the upper level is busy, the same as the rest, the usual rotary…
Telephone
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