The invention provides tinted contact lenses that enhance or change the color of the lens wearer’s iris. The apparatus for performing the method includes at least one transmitter and at least one receiver. A direction determination unit determines the directions of the radio terminals viewed from the transmission unit on the basis of the signals received by the reception unit. Prior to path trace-back, the path prediction can be executed by utilizing the property that the minimum path metric and the path are consecutive. A moulded on resilient sealing ring is located around the central opinion through the motor plate for sealing between the motor plate and the armature shaft and a moulded on resilient O-ring is located on the face of the motor plate facing the bearing for engaging the outer race of said bearing.