in my mind this is a simple exercise. Take your sailing dinghy out in at dawn when the first breeze is in the process of forming. She's bobble around on the flat water, doing nothing,...doing nothing,...and then suddenly, as the wind increases incrementally -1kt-2kt-3kt- the 'sail' will quiver.

Do a little hunting with the rudder and the sheets, and the dinghy goes from bobbling to barely - but solidly - forward motion.

NOW QUICKLY! Reef your sails down! We're back to bobbling in the water,...doing nothing,...doing nothing,...Be patient, you'll be sailing soon with your less powered sailboat.

And this SA/D is no miracle. It's easy to achieve and you pay for it in having too much sail, very quickly. So a compromise is in order.

Interesting that they have applied different measurements over the years. That makes sense because the above situation - over powered - is the same today as it was centuries ago.

The compromise hasn't changed much, overpowered yesterday is still overpowered today.

In fact, in comparing apples to apples boats, we're still not moving a family of four in a cruising boat, much faster today than we did a hundred years ago. Length is still the dramatic Go Fast tool.