What operational feature should be verified last before securing the access door?

The correct answer is to verify frequency output last before securing the access door because it is essential to ensure the operational integrity of the equipment being used. Frequency output is a critical parameter that indicates whether the system is functioning effectively within its designed parameters. By checking this last, you can confirm that all systems are operating normally and that the frequency aligns with operational expectations, thereby minimizing the risk of issues arising after securing the access door.

In addition, verifying frequency output at the end helps ensure that any recent changes in operation or adjustments have stabilized and are functioning correctly before the equipment is secured. This final check serves as a safeguard against potential malfunctions that could arise from incorrect frequency settings. Thus, it provides confidence in the reliability and readiness of the system before it becomes inaccessible once the access door is secured.