#Tide Tables.# Brief information as to the time and height of the tide is usually for convenience given on the face of the chart. More complete information is published in the Tide Tables, with which every navigator should be provided. "The Tide Tables for United States and foreign ports," published annually in advance by the United States Coast and Geodetic Survey, give complete predictions of the time and height of high and low water for each day of the year for 70 of the principal ports of the world, and the tidal differences from some principal port for 3000 subordinate ports. The other leading nations also publish annual tide tables; those of the British government are entitled "Tide Tables for British and Irish ports, and also the times of high water for the principal places on the globe." #Light and buoy lists.# Brief information as to all artificial aids to navigation is shown on the charts. Every vessel should also have on board the latest official light and buoy lists, which give a more detailed description than can be placed on the charts. Light and buoy lists for the coasts of the United States are published annually by the Light-House Board. The United States Hydrographic Office publishes a "List of Lights of the World" (excepting the United States), in three volumes. The British Hydrographic Office publishes eight volumes of Lists of Lights, and these are corrected annually. #Chart catalogues# are published in connection with all series of charts. They give the particulars and price of each chart published, and are usually arranged in geographical order, with both alphabetical and numerical indexes, for convenience in finding charts either by position, name, or number. #Charts for special purposes.# There are various special charts published for the benefit of mariners, although not intended for direct use in plotting the course of a vessel or in locating its position. Some of the more important of these are mentioned below. #Gnomonic charts# are intended solely for laying down the great circle or shortest practicable courses between points, for which purpose they are very convenient. Their use has already been described. The United States Hydrographic Office publishes six such charts, for the North Atlantic, South Atlantic, Pacific, North Pacific, South Pacific, and Indian Oceans. #Current charts# are published by the British Hydrographic Office for the various oceans; these usually show the average ocean currents, but for the Atlantic there are monthly and for the Pacific quarterly current charts. #Magnetic variation charts# are published by both the United States and British governments. They show on a mercator chart of the world the isogonic lines, or lines along which the variation of the needle from true north is the same. The lines are drawn for each degree of variation. The annual change in the variation is also indicated.