NOVELTY - The device has a central base unit (55) adapted for mounting on trunk of a user and a positioning element arranged for connection to a limb. The positioning element is operatively connected to the central base unit for determining the position of the limb with respect to the central base unit. The central base unit is operatively connected to the positioning element through a flexible unit. The positioning element comprises a limb connecting element and a position transducer. The position transducer comprises a distance determining instrument and an angle determining instrument.    USE - Person mountable limb position determining device for determining the position of one or more limbs of a user relative to body, for use with interactive software of an exercising system (claimed), and computer gaming device such as jogging game apparatus.    ADVANTAGE - The central base unit is mounted on the trunk of the user carrying the device, thus enabling the user to move free on the ground without influencing the position determination of the limbs with respect to the central base unit. The device connects the central base unit operatively to the positioning element through flexible or wireless units, thus enabling the user carrying the device to move the limbs freely during usage of the device. The device reduces the distance between the central base unit and the positioning element, thus providing reliable communication, higher power efficiency and small delay. The central base unit is adapted for cooperating with two or more positioning elements, thus reducing the size of the device. The positioning element comprises a limb connecting element and a position transducer, thus enabling the positioning element to be easily mounted on the limb through a limb connecting element. The central base unit is provided with a data gathering unit for processing data provided by the positioning element, and a sender for sending the data to a receiver for further processing, thus simplifying data communication.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for an exercising system comprising a receiver for receiving data provided by a position determining device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a person mountable position determining device.    Central base unit (55)    Belt (56)    Ultrasonic transducers (57-60, 65-67)    Limb connecting elements (61-64)