To make high quality barcodes, several work-arounds have been adopted by barcoding software:
Require the use of high-resolution printers
Require the user of Magic Numbers as NarrowBarWidth
Force the use of pixels as length units
The pixel size of a high resolution device is too small to be noticeable by even high resolution scanners. The overall accumulation of rounding errors is small. The barcode printed is also very accurate - meaning that you can always achieve the size you want on a high resolution printer.
Another way is to make the width value closest to integral times of a pixel length. Our testing found that this approach worked very well when the bar code element width occupying at least 2 pixels. Based on this theory, when you carefully select the element width value you can still achieve a grade A barcode on a low-resolution printer.
Some software only work with specific barcode printers. They work around the issue by allowing user to enter the length values in the number of pixels. The problem with this approach is that the barcode data is only meaningful to certain category of printers. The barcode data is not portable.