The testo 420 app is a free, flexible, and mobile utility tool that complements the testo 420 flow hood. It offers practical functions that enable quick and easy measurement, documentation, and reporting of results. The app works with smartphones and tablets and offers features such as measuring current values, creating PDF and CSV reports, calculating total volume flow and air exchange rate, adding comments and photos to reports, sending reports directly via email, and identifying system changes through graphical trend display. The app communicates via Bluetooth Low Energy with a range of about 20m. For full functionality, download the Testo Smart App, which is designed to work together with the testo 420.