to the units of measurement used for the input values entered into the formula. This has led to the idea that the use of metric units for the formula represented a major concession on the part of the British whose preeminence in yachting at the time could have justified using Imperial units. In fact, the formula works equally well with Imperial Units. The relation between the length and area components of the formula are preserved whether in metric or Imperial Units. The use of the term Metre refers to the unit of length used in the expression of the result of the calculation. If one uses Imperial Units, the result for a Six Metre yacht is 19.685 feet. The London Conference preferred the term "Six Metre" yachts to "19.685 Foot" yacht. Why doesn't the "number" correspond to a yacht's length? For the International rule, the rating number is approximately equal to the sailing length of the hull. These boats have long overhangs which allow the waterline length to increase as the boat heels over. A displacement hull's maximum speed (the hull speed) is directly proportional to the square root of its waterline length. The first rating rules were first expressed as the weighted sum of various speed factors such as length and sail area. Later rules included resistance factors, such as draught or freeboard. These resistance factors could either be subtracted from the speed factors or used as divisors of the speed factors. Some rules thus took the form of fractions—some "trivial", where the divisor was merely a constant, and others "non-trivial", where the divisor was a resistance factor. The Union Rule was a trivial fraction (the divisor being "150") and the Universal Rule non-trivial (the divisor being 5 times the cube root of the draught). It was the illustrious architect, Dixon Kemp, who began the tradition of expressing British rules as trivial fractions with a divisor of "2", thus starting the tradition of the age old question: "Since your boat is a Six metre, why is it 12 metres long?" Metre classes While many different Metre Class yachts were constructed during those first heady years, of the sizes specified in the original rule, four have maintained their popularity; the 5.5, 6, 8 and 12 Metre Classes. The year after the ratification, the 12 Metre Class were chosen for the Olympics—the 6 Metre and the 8 metres were also used