Method, means, portable terminal accessory and system for calibrating a sensor device comprising a positioning unit detecting the position of the electronic device, an image capturing unit capturing an image of the environment around the electronic device, a processing unit detecting the presence of at least one identifiable object in the image captured and from a comparison of the position of the object in relation to the position of the user determining the heading of a user of the electronic device. Once the heading of the user is determined, it is used to calibrate one or more sensor devices or sensor functionalities in the electronic device.