CowBell Labs aims to make agricultural methane measurements accessible and trustworthy. They require low-cost methane emission test standards to calibrate their sensors. The CowBell Labs team designed a custom mass flow controller using low-cost off-the-shelf flow sensors, discretized flow approaches, and feedback control. The team’s custom emitter covers four orders of magnitude of flow rates and disperses the released methane over a wide area to mimic diffuse agricultural emissions.