A sole for aerated footwear having an elongate body with a lower surface, a device attached to the body, and an operating member, arranged to move away from and towards the body in a direction transverse to the longitudinal extent of the body as the sole bends to disengage and unbends to engage a floor, for operating the device. The application enables a handheld computing device to transfer a user’s various online account credentials to a user’s other computing devices securely and automatically. One step includes constructing a perturbation model relating changes in control parameters for the apparatus to one or more resulting changes in the process.