As a recognized leader in airflow control for critical spaces, Phoenix Controls is often asked to comment on the use of flow measurement devices. Our equipment does not measure flow. In fact, when other system suppliers claim to be measuring flow, they are not directly measuring flow in these applications. Instead, the flow is estimated using velocity pressure, static pressure drop across a restriction, or pressure variation frequency, and translating that measurement thorough the use of pressure transducers. While these techniques are based on sound physical principles, the process of using these measurements to maintain highly accurate flow control is fraught with significant real-world challenges as described in this white paper.