First-Layer Squish Guide
Almost every early print failure traces back to this one layer — here's what correct actually looks like.
Reading the first layer
Too high (not enough squish): individual lines look round and don't touch their neighbors, with visible gaps between them. Poor adhesion, may not stick at all.
Correct: lines are slightly flattened, touching their neighbors with no visible gaps, but you can still make out that they're individual lines rather than one solid sheet.
Too low (too much squish): lines are pressed flat into a solid, almost translucent sheet, sometimes with a rough or scraped texture, and the nozzle may make an audible dragging or grinding sound.
Z-offset vs. bed leveling — different problems
Bed leveling makes the nozzle-to-bed distance consistent across the whole bed; Z-offset sets what that consistent distance actually is. A perfectly level bed with the wrong Z-offset still prints a bad first layer, evenly bad across the whole surface rather than worse in one corner — that's the tell for which problem you actually have. See the Bed Leveling Guide if the issue instead varies noticeably from one area of the bed to another.
Adjusting in small steps
Z-offset changes are usually made in increments of 0.02–0.05mm at a time — it's a small enough distance that "a little too much" adjustment overshoots from one failure mode straight into the other. Most printers let you adjust Z-offset live during the first layer of a test print; watch the line quality change in real time rather than guessing a value, printing a whole model, and starting over.