Instruments that both measure a parameter and automatically regulate a process (e.g., a flow controller) can be classified either as measuring instruments or as automatic regulating apparatus, which fall under different Chapter 90 headings with different duty rates. The classification turns on whether the control function or the measurement function is primary, and CBP has issued binding rulings on this distinction — making advance ruling requests a prudent step for high-value shipments.

Most industrial measuring and control instruments do not require FDA review. However, instruments intended for in vitro diagnostic use or for direct patient monitoring may be regulated as medical devices under FDA jurisdiction and require appropriate registration and clearance before importation. Importers should confirm the instrument's intended use and consult with a customs broker or regulatory counsel if medical device classification is possible.