Internal seam dimensions are measured and calculated from a cross section of a double seam:
These values determine if the closed seam is sealed properly.
What to do if the Internal values are out of specification?
Assuming that the Seam inspection system SEAMetal and SEAMscan is calibrated, then usually the problem is in the 1st operation or 2nd operation and the Seamer will require a seamer setup. This can be done either using feeler gauges or using a clearance gauge.