DIN

I don't care if this blog is terminated. I will add some reflexions, anyhow. The German Industry Standards of paper format is a geometrical series of rectangulae, beginning with A0, which has an area of one square metre. "A1" is half this area, and has the same shape. This can be accomplished in one unique way.

This is the ISO_216 standard. In some countries, where the metric system does not apply, other formats are in use.

Those of my readers, who do not accept the metre, should at least agree with this: A square can be divided into two equal parts, by drawing a diagonal. Hence we can easily construct a square, having half the area of a given one. This is mathematics, rather than metrology.