What agency has the primary responsibility for periodically calibrating test, measurement, and diagnostic equipment?

The Precision Measurement Equipment Laboratory (PMEL) is the correct answer because it is specifically designated to ensure that test, measurement, and diagnostic equipment (TMDE) is accurately calibrated and maintained. PMELs are responsible for conducting the calibration procedures and ensuring that all equipment meets established accuracy standards required for operations in the military and other technical environments.

The PMEL provides the necessary expertise and specialized facilities to handle the calibration of various types of equipment, which is crucial for maintaining operational readiness and reliability. Regular calibration by PMEL ensures that all measurements taken are consistent and traceable to national standards, which is vital for both safety and effectiveness in missions involving aircrew and other military operations.

While other agencies or offices may have roles that intersect with calibration efforts, none match the PMEL's focused mission specifically dedicated to this task. Therefore, the high level of specialization and the clear, defined responsibility of the PMEL solidifies its status as the primary agency for this essential function.