The present invention relates to a process for the co-production of ethylene and propylene from an ethanol feedstock and a propanol feedstock. The primer layer is obtained by applying, to the surface to be treated, a latex consisting of structured particles of polymers having a range with a soft character and another range with a hard character. The roles and responsibilities of participants in the community of practice are identified. The back cover attaches to the back of the smartphone and has an interface for accepting a breath from a user and routing the breath through at least one channel such that the breath is fluidly interfaced between the interface for accepting the breath and the pressure sensor.