pilot to find the strongest lift. On cross-country flights on days when strong lift is forecast, pilots fly with water ballast stored in tanks or bags in the wings and fin. The fin tank is used to reduce trim drag by optimizing the center of gravity, which typically would shift forward if water is stored only in the wings ahead of the spar. Ballast enables a sailplane to attain its best lift-to-drag ratio (L/D) at higher speeds but slows its climb rate in thermals, in part because a sailplane with a heavier wing loading cannot circle within a thermal as tightly as one with a lower, unballasted wing loading. But if lift is strong, typically either from thermals or wave, the disadvantage of slower climbs is outweighed by the higher cruising speeds between lift areas. Thus, the pilot can improve the average speed over a course by several percent or achieve longer distances in a given time. If lift is weaker than expected, or if an off-field landing is imminent, the pilot can jettison the water ballast by opening the dump valves. On days with particularly strong and widespread lift pilots can attain high average speeds by alternating periods of fast flight with pull-ups, merely slowing down in areas of lift without deviating from the course. This 'dolphining' technique can result in high average speeds because the height lost can be minimised until particularly strong lift is encountered when circling would be most effective. Badges Achievements in gliding have been marked by the awarding of badges since the 1920s. For the lower badges, such as the first solo flight, national gliding federations set their own criteria. Typically, a bronze badge shows preparation for cross-country flight, including precise landings and witnessed soaring flights. Higher badges follow the standards set down by the Gliding Commission of the Fédération Aéronautique Internationale (FAI). The FAI's Sporting Code defines the rules for observers and recording devices to validate the claims for badges that are defined by kilometres of distance and metres of altitude gained. The Silver-C badge was introduced in 1930. Earning the Silver Badge shows that a glider pilot has achieved an altitude gain of at least , made a five-hour duration flight, and has flown cross-country for a straight-line distance of at least : these three attainments are usually, but not invariably, achieved in separate flights. A pilot who has earned the Gold