Having tried to print a physically-accurate scale on a non-commercial printer I would be surprised if a 1x1inch box actually measures the same in real life.

I’m confused and not sure what you mean. The device knows what size it’s printing at (e.g. A4 which is 210×297mm). One some devices with bad feeders you might get local error up towards 1% in the feed direction (probably <1‰ in the perpendicular), but on decent printers it’ll always be well below 1%.

If what you printed wasn’t accurate, something else was at play.

Yeah it knows it's printing A4, but it can't print edge-to-edge, if you print a black rectangle the white borders are not a uniform size.

If you created a document using an A4 template and measured objects within this document using millimetres, when printed the objects would not be printed at exactly that size.

I know this because I've tried to do exactly that, and tried various permutations - on my specific printer I found that the warping was sometimes non-linear along the vertical axis! Maybe I've just got a particularly crap printer... Oh, Brother!

Being able to print edge-to-edge is not necessary, and is mostly to do with practical feeding limitations. Alignment on the sheet is also allowed to suffer. But of what it does print, I’ve printed and observed printed a number of precise things on several different printers (mostly lasers, but at least one inkjet and a phaser, way back) with no visible warping. ¯\_(ツ)_/¯