if 0 {[Richard Suchenwirth] 2002-12-29 - ''Letter'' and ''Legal'' paper
formats are popular in the US and other places. In Europe and elsewhere,
the most widely used paper format is called ''A4''. To find out how big
a paper format is, one can measure an instance with a ruler, or look up
appropriate documentation. The ''A'' formats ([DKF] - I believe these are
defined in a [DIN] document somewhere...) can also be deduced from
the following axioms:
   * A0 has an area of one square meter
   * A(n) has half the area of A(n-1)
   * The ratio between the longer and the shorter side of an A format is constant

How much this ratio is, can easily be computed if we consider that A(n)
is produced from A(n-1) by halving it parallel to the shorter side, so
 2a : b = b : a, 2 a2 = b2, b=sqrt(2) a, hence b : a = sqrt(2) : 1
So here is my implementation, which returns a list of height and width in
centimeters (10000 cm2 = 1 m2) with two fractional digits, which delivers a
sufficient precision of 1/10 mm:
}
 proc paperA n {
    set w [expr {sqrt(10000/(pow(2,$n) * sqrt(2)))}]
    set h [expr {$w * sqrt(2)}]
    format "%.2f %.2f" $h $w
 }
 % paperA 4
 29.73 21.02

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Detailed info on the format A, which is from [ISO] 216, can be found here [http://www.cl.cam.ac.uk/~mgk25/iso-paper.html]. [Michael Schlenker]