An extremely useful set of cards which makes a difficult subject much easier. Each card shows a vessel's display of night-time navigation lights (in colour) or daytime shapes, as seen from your position. In the case of the cards showing lights the vessel's silhouette is just discernible. The meaning is shown on the back of the cards as usual. This set has been a "best seller" for over 20 years because learning the lights and shapes is a major part of a mariner's study and without Flip Cards it's not easy.