A selection device for setting the driving speed of a vehicle is provided having an operating element, a control device, which is connected with the operating element and coupled with an engine control and which is designed so that, upon activation of the control, the vehicle speed will be regulated automatically, whereby at least two vehicle speed values can be marked on a display. The first guide wire can pass through the first cannulated insertion instrument such that a first end and a second end of the first guide wire extends beyond the first end and the second end, respectively of the first cannulated insertion instrument. In other words, the correction part controls the quantity of the object supplied to a dispersion feeder on the basis of measured data indicating an actually measured value. A database holds information about each rail segment.