The 10 Rater class of model yachts is based on the length by sail area rule of 1887. Shortly after this rule was adopted for rating full sized yachts, model builders began using the rule as a foundation for new boat design. The 10 Rater class is unique in its method of "rating" yachts, where the only two parameters that matter are waterline length and total sail area. However, as each parameter contributes toward boat speed, their relationship may only change inversely: as one goes up, the other must go down. This allows 10 Raters to be highly specialized for local performance, or in the most extreme sailing conditions worldwide. The present 10 Rater class-rating rule allows builders the greatest freedom to experiment with performance improving design and technology.