Pythagoras did not, but it is a simple rule of physics. I will get back to the notion of the A0 and the standard square metre. If you look at a ream of paper—500 sheets in the metric system—it will often have a GSM measure on it. It may be 80 GSM, 120 GSM or 200 GSM. Essentially that means, for example, that the paper is 80 grams per square metre. That means that every A0 sheet in the shape of the golden rectangle is that weight. From that you can then calculate the weight of a printed item. It certainly adds to our efficiency in transport when we have standards of measurement.