External double seam dimensions
External dimensions include all the values of the seam that can be measured externally with a micrometer. These are not to be confused with visual seam defects.
Typically, the external dimensions are measured while the can is still closed and pressurized:
When measuring on an open (cut) seam, the values might expand a bit due to the loss of pressure when opening the can and the act of cutting it, however modern seam inspection software can compensate for each of these and produce the very same measurements using an optical unit.