Out-of-tolerance flatness is a high-frequency source of sheet and plate complaints. When locating the cause, work backward through the process steps:

- The shape and internal stress of the hot-rolled/cold-rolled incoming material itself. - Worn leveling rolls or improperly set tension on the cut-to-length line. - Local warping caused by heat input from laser/plasma cutting. - Deformation caused by improper stacking or vertical storage during storage and transport.

At acceptance, the measurement method should be agreed upon (surface plate plus feeler gauge, measurement positions, tolerance values); otherwise the two parties will each have their own account. For parts that will later be welded or bent, flatness requirements should also be specified at the time of purchase, rather than looking only at thickness tolerance.