Abstract: A correction unit (13) for correcting the position of a side plate (2,2?) of a screed (4) of a road paving machine (1) for constructing a road pavement relative to a line (12) on an underlying surface on which the road paving machine (1) is adapted to move, the correction unit (13) comprising a sensor device, where the sensor device is adapted to sense at least part of said underlying surface comprising the line (12) and identify a displacement of the side plate (2,2?) of the screed (4) of the road paving machine (1) relative to the line (12) on the underlying surface and provide a sensing signal for controlling the position of the side plate (2,2?).