The new testo 420 volumetric flow measuring hood is the lightweight, precise and convenient solution for controlling volumetric flows at larger air inlets and outlets. Especially at swirl diffusers, the flow rectifier significantly reduces common measurement errors. This enables users to quickly and precisely comply with hygienic guidelines and specifications for room air quality in ventilation systems, e.g. in industry, offices or clean rooms. With a uniquely low weight of less than 2.9 kg and ergonomic handles, handling is particularly easy. For a more comfortable reading of the measured values, the measuring device can be tilted and removed. In addition, mobile devices can be used as a second display and remote control by means of app connection via Bluetooth. For example, the use of a tripod is particularly safe and convenient for high ceilings. In addition, users can finalize and send the measurement report directly on site using the app.