Gas measurement using Daniel box.

Daniel box is used to measure gas flow rate. it holds or carries an orifice, so by passing gas via the opening, a pressure drop takes place. The upstream and downstream are measured and recorded. The former represents the static, and the latter represents the differential.
Multiplying these values with other coefficients gives the gas rate per day.
It could be installed on compressor discharge, gas line in gas lifted well as in the video and the gas outlet in test separator.

[@GuardianAngel2023]

Nice explanation