Understanding conductance, Ce in compressed air flow

Aug 2019
I'm looking at classifying air flow characteristic of pneumatic components and I've decided to follow an ISO standard (ISO:6358). It states that the flow rate is a related to the inlet and outlet pressure \(\displaystyle \frac{p_{2}}{p_{1}}\), which would make since for compressible flow. For a component the conductance \(\displaystyle Ce=\frac{q_{v}}{p_{1}} \sqrt{\frac{T_{1}}{T_{0}}} =\frac{q_{m}}{\rho_{0} p_{1}} \sqrt{\frac{T_{1}}{T_{0}}}\) where \(\displaystyle q_{v}\) is volume flow rate at standard conditions, \(\displaystyle q_{m}\) is mass flow rate at actual conditions, and the subscripts denote \(\displaystyle 1\) are inlet conditions, and \(\displaystyle 0\) are standard conditions.
I was wondering if anyone knew where this relationship is derived?
The experimental setup is basically a pressure drop experimental system that has the capabilities to record standard condition flow rate, temperature and pressure at inlet and outlet locations of the component under test.
Oct 2017
Sorry, no idea. My fluid mechanics textbook specifies a lot of mathematics related to compressible flow ducts and other different geometries and with different flow conditions (depending on Mach number), but no mention of conductance.