What is the purpose of an order-wire circuit in communication systems?

The purpose of an order-wire circuit in communication systems is primarily for operator-to-operator service messages. This circuit facilitates the communication and coordination between operators, allowing them to communicate operational information such as instructions, status updates, or any necessary messages related to the functioning of the communication system.

Order-wire circuits are essential for maintaining effective communication, especially in systems where quick and clear dialogue among operators is critical. They are not used for broadcasting content like music, which is why that choice does not apply here. Similarly, frequency modulation and automatic tuning focus on signal transmission and reception quality rather than direct operator communication, thus not aligning with the primary function of an order-wire circuit.