To obtain all the available information from radar when visibility is poor, it is widely recognized that plotting is essential. No doubt plotting is carried out whenever possible, but in many merchant ships at sea today the ideal has limitations due to manning difficulties. Where the master has only one officer on the bridge to assist him it is not easy to cope with all bridge duties and carry out plotting in the usual way. To obtain full and accurate information a plotting officer must give his undivided attention to make use of the three known elements, range, bearing and own speed in order to produce the other ship's course, speed and nearest approach and follow up with the change of course and speed that may be required to keep out of the region of collision.