What should you press to acknowledge receipt of a message during a PJM All Call?

To acknowledge receipt of a message during a PJM All Call, pressing "2" is the correct action to take. This protocol ensures that participants confirm they have received important information, which is critical for maintaining effective communication during emergency situations or significant announcements. Acknowledgment through this method helps PJM maintain a clear understanding of who is present and who has received vital messages, ensuring all stakeholders are informed and can take necessary actions based on the received information. Understanding the specific key for acknowledgment is important in the context of PJM operations because it enhances coordination and response effectiveness among participants.