let me throw out another benefit that Portsmouth has over a measurement based system.

Take the Hobie 16 and the F16. There is a philosophical class difference that affects the boat speed and the related rating (no, I'm not talking about the spinnaker). The Hobie 16 sail plan and sail material does not evolve (mostly) and is not open to different sail manufacturers. The F16 on the other hand does and is. F18 has seen quite an evolution in sails and speed potential. Portsmouth can handle this difference readily. A measurement system cannot without manual manipulation.