A method includes opening a flow path from a gas stick through a variable orifice, a chamber, and an outlet isolation valve of the chamber. The method further includes causing a gas to flow through the flow path at a flow rate setpoint. The method further includes actuating an opening of the variable orifice to establish a choked pressure regime within the chamber, the choked pressure regime being achieved by causing a first pressure upstream of the variable orifice to be at least two times a second pressure downstream of the variable orifice. The method further includes closing the outlet isolation valve to cause the chamber to be filled with the gas from the gas stick. The method further includes measuring a pressure rate-of-rise within the chamber. The method further includes determining one or more flow measurements based at least in part on the pressure rate-of-rise.

A system for mounting a differential pressure indication device for indicating a presence of a directional differential pressure between a first space and a second space separated from the first space by a barrier is provided. The system may include a base configured to be mounted against the barrier, where the base includes a receptacle configured to removably receive the pressure indication device. The system may include at least one mounting fastener configured to removably secure the differential pressure indication device within the receptacle. The system may include a pitch adjuster configured to secure the base to the barrier, where movement of the pitch adjuster is configured to adjust a spacing between a portion of the base and the barrier to adjust the orientation of the base with respect to pitch.