Print issues #1: It's all about the ISO
     Welcome to a new series of post. After the Graphic design history review we did during the last year this year we will talk about print issues: paper, color, tutorials,...
This first post will be related to paper sizes, the ISO formats, how it works and why we use them.
Many paper size standards and conventions have existed at different times and in different countries. Today there is one widespread international ISO standard (including A4, B3, C4, etc.). The paper sizes affect writing paper, stationery, cards, and some printed documents. The standards also have related sizes for envelopes.
ISO paper sizes are all based on a single aspect ratio of square root of 2, or approximately 1:1.4142. The base A0 size of paper is defined to have an area of one m². With the given aspect ratio of square root of two, this corresponds to a piece of paper which its longer side is one metre multiplied by the square root of the square root (that is, the fourth root) of two and the shorter side being the inverse of this value. Rounded to millimetres the A0 paper size is 841 by 1,189 millimetres (33.1 × 46.8 in).
Successive paper sizes in the series A1, A2, A3, and so forth, are defined by halving the preceding paper size along the larger dimension. The most frequently used paper size is A4 (210 × 297 mm).
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ISO 216 defines the A series (for almost anything: posters, design, magazines, stationery, notebooks or postcards) of paper sizes based on these simple principles:
The height divided by the width of all formats is the square root of two (1.4142).
Format A0 has an area of one square meter.
Format A1 is A0 cut into two equal pieces. In other words, the height of A1 is the width of A0 and the width of A1 is half the height of A0.
All smaller A series formats are defined in the same way. If you cut format An parallel to its shorter side into two equal pieces of paper, these will have format A(n+1).
The standardized height and width of the paper formats is a rounded number of millimeters.
For applications where the ISO A series does not provide an adequate format, the B series (for books) has been introduced to cover a wider range of paper sizes. The C series (for envelopes) of formats has been defined for envelopes.
The width and height of a Bn format are the geometric mean between those of the An and the next larger A(n−1) format. For instance, B1 is the geometric mean between A1 and A0, that means the same magnification factor that scales A1 to B1 also scales B1 to A0.
Similarly, the formats of the C series are the geometric mean between the A and B series formats with the same number. For example, an (unfolded) A4 size letter fits nicely into a C4 envelope, which in turn fits as nicely into a B4 envelope. If you fold this letter once to A5 format, then it will fit nicely into a C5 envelope.
B and C formats naturally are also square-root-of-two formats.
 Press business will use RA and SRA formats. They are made based on ISO formats but a little bit bigger so the cut doesn't affect the printed zone. To get printed an A1 (841x594mm) the design may be printed on a SRA1 (900x640mm).