One very reliable approach to establishing air quantity through a ventilation branch is through measurement of differential pressure across an opening or regulator. Mathematical relationships are available to relate (with some qualifications) pressure drop and quantity through an orifice placed symmetrically in a round flow conduit. However these can only be used to approximate mine regulator behaviour due to variability in construction, questions of symmetry and leakage Efforts to characterize and/or mathematically model a number of types of operating mine regulators are described. Results can be used in the development of a computerized monitoring and simulation system to provide immediate or real time data on air behaviour within each branch within an underground mine ventilation network through linking of sensors to the ventilation network simulation software. This new approach to ventilation provides improved understanding of airflows through all mine sections.