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How to mitigate the freedom to measure anything by citizen using microsensors and the strict metrological protocol characteristic of the expert world of the official air quality surveillance association (Association Agréée de Surveillance de la Qualité de l’Air or AASQA)? The Checkbox project was issued by two sociologists and a local AASQA (Atmo Aura). It consisted in lending microsensors to 70 people located in 3 different territories during 3 annual campaigns to freely measure air particulate matters, with a special focus on wood heating. The paper describes the project’s conception and how it lies between citizen creativity, imaginaries, and measurement freedom, and metrological expertise of Atmo Aura. It opens new venues for taking into account the diversity and reliability of practices as soon as the metrological expertise is extended to other publics and the criteria of accuracy and legitimacy are modified. What contributors judge as what is expected in Checkbox is instrumental in the way they conduct measurement and how they account for it.