This rotation may be used to create microwave devices as isolators, circulators, gyrators, etc. Circuitry in telephone exchanges has also been affected with gyrators being used in line cards. This method returns a synthesis using the minimum number of resistors and contains no gyrators. Gyrators can replace them in many applications. Cascading two gyrators achieves a voltage-to-voltage coupling identical to that of an ideal transformer. From the point of view of network theory, transformers are redundant when gyrators are available. In particular, gyrators make possible network realizations of isolators and circulators. Gyrators are used in most DAAs (data access arrangements). Gyrators do not however change the range of one-port devices that can be realized.