From: Philippe VERDY (verdy_p@wanadoo.fr)
Date: Wed May 18 2005 - 10:13:29 CDT
> The motivation for the sqrt(2) ratio: if you fold a piece of A paper in two, you get exactly an A piece. Thus you can print two A4 pieces side by side on an A3 piece, without margins. If you scale up an A4 piece, you can fit precisely an A3 piece, without margins (and conversely). Combine the two, and you can print two A4 pieces side by side, scaled down, on one A4 piece, without margins. Very convenient.
>
> The motivation for one of the A = 1 square meter: the metric system.
>
> The motivation for the actual dimensions: given the constraints above, 297 x 210 is close to 270 x 210, the previously used common size (at least in France). I don't know where that older standard comes from.
I've never seen and used 21x27cm paper. If it has existed, it may be because of bad spelling when commanding paper reams of 21x29,7cm.
Or because 21x27cm resulted from detachable bands of roughly 1.5cm with glue on a standard A4 paper, or to avoid cutting the folded paper sheet inserted in a DL envelop.
Don't forget the other common format used for (and a bit expensive, but not as much as paper used for printing photography...) paper "Canson" (tm) used in many schools in France for artistic works (called "collèges" for teenagers below 15, and "lycées" in the last 3 years before the bacchelor graduate): 24x32cm.
It seems that this 3:4 (vertically) format fits better for portrays and (horizontally) landscape scenes. For many decenials Canson was the only provider of this paper recommanded (required in the past) by school professors. I think there may exist other marks today, and no requirement for the exact format to use in arts lessons. Beside this, this paper was really bad to paint, as it was too much absorbant, and the colored inks were drifting around within the paper structure (and there was no way to erase a line drawn with a carbon pen without altering its structure; no error was possible, or you had to use your pen VERY lightly).
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