Two cabinets with a 0.3 mm difference in height do not show as a 0.3 mm step. They show as a shadow line several pixels wide, because the light from the modules grazes the edge and the mask casts it across the neighbouring module.
The geometry
A viewing angle of 30° off-axis turns a 0.3 mm step into a shadow roughly 1.5 mm wide on the adjacent surface. At P2.5 that is more than half a pixel — enough to read as a dark seam along the whole cabinet edge.
At 5 m viewing distance, the human eye resolves about 1.5 mm at that range. The seam is right at the threshold, which is why some clients see it and some do not, and why arguments about it never resolve cleanly.
What actually controls it
- The cabinet tool. ±0.1 mm and ±0.3 mm cabinets are different products from different moulds. A supplier quoting ±0.1 mm and shipping ±0.3 mm is not lying about the number, they are quoting the tool they wish they had.
- Mixing tools. Two cabinets from two moulds will not mate flush even if both are individually within tolerance. Buy modules and cabinets as one set from one production run.
- The frame. A frame that is not flat imposes its own error on every cabinet bolted to it. Check the frame with a laser before the cabinets go on, not after.
- Installation torque. Over-tightening the quick-locks pulls the cabinet face out of plane. We specify a torque and most crews ignore it.
The test to run before accepting delivery
Assemble four cabinets on a flat floor, face up, and put a straight edge across the seams with a backlight behind it. If you can see light under the straight edge at any point, the wall will show a seam. Do this before the container is loaded, not after it clears customs.
What to do when the budget is tight
If the wall is above 10 m viewing distance, a ±0.3 mm steel cabinet is genuinely fine and costs about 25% less. The mistake is buying ±0.3 mm for a street-level screen and then trying to fix it with calibration. Brightness adjustment cannot hide geometry.