The testo 327-1 Flue Gas Analyser offers a robust and simple entry into flue gas analysis for domestic boilers. It measures O2 & CO , and will calculate ratio, CO2, etc. The 4-line LED display can be configured to the users requirements, and its back-lighting function guarantees an easy-to-read display even if lighting conditions are unfavourable. The analyser stands out on account of its easy menu navigation and ergonomic housing as well as its durability.