...although you need to beware of printouts getting silently scaled. It's really common, when someone asks to print (e.g.) an A4-sized PDF to A4 paper, for the

...although you need to beware of printouts getting silently scaled. It's really common, when someone asks to print (e.g.) an A4-sized PDF to A4 paper, for the printer driver to rescale it so that the entire document (including margins) fits within the (slightly smaller) printable area of the device. "Shrink to fit [within printable area]" seems to be a common default setting. (If you're using PDFs for precisely-scaled engineering drawings, I expect you're well aware of this and have a workflow that avoids scaling, but I see people trip over it all too often.)