Three kinds of steering-gear are used, the weighted swinging rudder, the main-sheet balance gear, and the steering vane, the object of each being to keep the model on a true course, either before or against the wind. Models are often sailed without dynamic control of the rudder, but although a perfectly built boat will sail readily against the wind without steering gear, it is almost impossible to keep it on its course before the wind without some contrivance to check for divergence. The setting of the steering gear and sheet positions must be adapted to the wind conditions and this is a subtle art to master. These controls are the traditional methods, for more than 100 years before the advent of radio control and they continue to be used worldwide.