A false seam is essentially the worst kind of problem you can have in a double seam… From the outside, the Seam Thickness and Length appear to be correct, but there is no hermetic seal. This is why sectioning (cutting) the seam is so critical in evaluation!
Examples of actual real life False seams as they appear in a computerized seam scope.
False seams may sometimes appear on the outside of the can – typically identified as “Vee“, “Droop“. However, this can be missed, which is why 360 degree non-destructive scanning or the combination seam gauge of the cans can be extremely useful.