The tax law obligations of other parties, such as the recipient of a tax invoice, must also be considered. When base records, such as invoices and receipts, are maintained in Māori there may be some inconvenience to other persons. GST tax invoices and debit and credit notes raise a specific issue. They are necessary for ascertaining the tax liability of the issuer and of that other party. They are, therefore, records covered by section 75(3) of the GSTA that must be maintained in English, unless the Commissioner gives permission to use another language.

The magnification factors between all A sizes: from to A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A0 100% 71% 50% 35% 25% 18% % % % % % A1 141% 100% 71% 50% 35% 25% 18% % % % % A2 200% 141% 100% 71% 50% 35% 25% 18% % % % A3 283% 200% 141% 100% 71% 50% 35% 25% 18% % % A4 400% 283% 200% 141% 100% 71% 50% 35% 25% 18% % A5 566% 400% 283% 200% 141% 100% 71% 50% 35% 25% 18% A6 800% 566% 400% 283% 200% 141% 100% 71% 50% 35% 25% A7 1131% 800% 566% 400% 283% 200% 141% 100% 71% 50% 35% A8 1600% 1131% 800% 566% 400% 283% 200% 141% 100% 71% 50% A9 2263% 1600% 1131% 800% 566% 400% 283% 200% 141% 100% 71% A10 3200% 2263% 1600% 1131% 800% 566% 400% 283% 200% 141% 100% Not only the operation of copying machines in offices and libraries, but also repro photography, microfilming, and printing are simplified by the 1:sqrt(2) aspect ratio of ISO paper sizes. Example 2: If you prepare a letter, you will have to know the weight of the content in order to determine the postal fee. This can be very conveniently calculated with the ISO A series paper sizes. Usual typewriter and laser printer paper weighs 80 g/m². An A0 page has an area of 1 m², and the next smaller A series page has half of this area. Therefore, the A4 format has an area of 1/16 m² and weighs with the common paper quality 5 g per page. If we estimate 20 g for a C4 envelope (including some safety margin), then you will be able to put 16 A4 pages into a letter before you reach the 100 g limit for the next higher postal fee. Calculation of the mass of books, newspapers, or packed paper is equally trivial. You probably will not need such calculations often, but they nicely show the beauty of the concept of metric paper sizes. Using standard paper sizes saves money and makes life simpler in many applications. For example, if all scientific journals used only ISO formats, then libraries would have to buy only very few different sizes for the binders. Shelves can be designed such that standard formats will fit in exactly without too much wasted shelf volume. The ISO formats are used for surprisingly many things besides office paper: the German citizen ID card has format A7, both the European Union and the . (!) passport have format B7, and library microfiches have format A6. In some countries (., Germany) even many brands of toilet paper have format A6. Further details Calculating the dimensions The ISO paper sizes are specified in the standard in a table that states their width and height in millimeters. Following the principles described above , the dimensions could be calculated with the following formulas: Format Width [m] Height [m] A n 2 −1/4− n /2 2 1/4− n /2 B n 2 − n /2 2 1/2− n /2 C n 2 −1/8− n /2 2 3/8− n /2 However, the actual millimeter dimensions in the standard have been calculated instead by using the above values only at n = 0, and then progressively dividing these values by two to obtain the smaller sizes, each time rounding the result to the next lower integer number of millimeters ( floor function ). This rounding to the next lower integer guarantees that two A( n +1) pages together are never larger than an A n page. The following programs demonstrate this algorithm in several programming languages:

- iso- – C version
- iso- – Python version