Are the dimensions consistent wrong through the entire print, or only on the first/last layer?
I’ve printed a few of the FDM 3D Printer Assessment test from the 3D Print Guide, Section 4.6 (I can’t link directly to the section, just the post). My first attempt received a score of 1 on the Fine Negative Features section. After printing a temperature tower and adjusting my retraction settings, I got it up to a 4.5 (I can remove the tightest pin, but only be lifting the pin out; I cannot drop the pin through the hole). That was printed with a 0.1mm layer height. The hangup on the tightest pin is when the top layer of the pin is flush with the hole. When I feel the pin, it is slightly mushroomed out on the top. If I trimmed up that top layer with a scraper, I’m sure if would fit through just fine. If I wiggle the pin in the hole, I can feel a small amount of slop. I only have analog calipers, so I can’t measure the pin and hole more accurately than about ±0.5mm.
That indicates that I can print in the X/Y axis with a max inaccuracy of +0.1mm. Most of that is either the top or bottom layer. For a project that I wanted very tight fitting pieces, I scraped the bottom layer with a metal ruler to remove the burr.