The value of plotting radar observations at sea has often been emphasized and some knowledge of the errors to be expected will be of use to the navigator. Small random errorsare always present in radar observations. Under certain conditions, particularly when ships are approaching end-on, even a correct interpretation of the observations can lead to a misinterpretation of the situation. The Steering Rules are operative only when vessels are in sight of one another, since if it cannot be assumed that there is a mutual understanding of the situation there can be no mutual rules of conduct.