The word user unit basically refers to the adjustment of different units in scaling. In connection with images and graphics, the size of the image is changed. Depending on whether it is a pixel or vector graphic, scaling can have an impact on the quality of the image.

There are the following differences between pixel and vector graphics:

• If a pixel graphic is now enlarged, the pixels of the image are also enlarged. Larger pixels also make edges appear more stepped, creating the so-called sawtooth effect.
• Vector graphics can be scaled to any size. Graphics can be enlarged without any loss of quality.

When we talk about user unit in the context of a PDF, we talk about the factor - 1:2, 1:5 or 1:10 etc. - which is applied to the effective page size in the output of the print file in the RIP.

As background information, you should also know the following statements about the user unit:

• The page length of a PDF can be a maximum of 200 inches (5,080 mm). PDF files that are larger than this must therefore include a scaling factor.
• User unit is technical jargon (PDF terminology) and means page scaling factor.
• User units can only be embedded in PDF files from version 1.6 and higher.
• Each page of a PDF file can have a different scaling factor.
• The value of the user unit is normally an integer. However, decimal places can also be processed.
• A page scaling factor can also be set for files whose page length is less than 200 inches.