The invention relates to a method for measuring and displaying data linked to a person's physical activity, comprising: measuring data linked to the person's physical activity using a mechanical sensor in a wrist watch worn by the person; displaying the measured data on the watch face; taking an image of the watch face using a camera in an electronic device; analysing the image in order to determine the data; processing the data so as to process the analysed data; and displaying the processed data on a screen of the electronic device.