Such devices are known in the prior art. In particular, portable electronic devices are known displaying an altimeter function, usually intended to be used when hiking.
However, in order to practise some activities, an indication of the altitude is not sufficient for the wearer of the device. In particular, in the practice of aeronautical sports involving piloting unpowered aircraft, it is important for the pilot to have information relative to his vertical speed of movement. The onboard instruments existing on transport aircraft present a large number of functions which are not all provided for the pilots of light aircraft of glider, microlite, para-glider or delta plane type.
Furthermore, in the practice of some other sports, such as parachute jumping, hiking or even mountain biking, the fact that the sportsman has available information about his altitude is useful and even essential in that which relates to free fall. However, it can be of interest to persons performing this type of activity to have complementary information available.