Abstract: An apparatus for quantifying a user's expiratory and inspiratory airflow includes an air tube adapted to be sealed over at least one of the nose or mouth of a user, a pressure sensor configured to be selectively fluidly connected with one of the air tube or an ambient environment external to the air tube, a valve assembly arranged between the air tube and the pressure sensor to switch between a measuring configuration in which the pressure sensor is fluidly connected with the air tube while fluid connection with the ambient environment is excluded, and a reference configuration in which the pressure sensor is fluidly connected with the ambient environment while fluid connection with the air-tube is excluded, and a data processing unit arranged to communicate with the pressure sensor and the valve assembly. The data processing unit is configured to provide instructions to the valve assembly to switch between the measuring and the reference configurations.