The numerical count position of a specific segment that is within the actual received message body. The numbering starts with, and includes, the UNH or the UIH segment as segment number 1. To identify a segment that contains an error, this is the numerical count position of that segment. To report that a segment is missing, this is the numerical count position of the last segment that was processed before the position where the missing segment was expected to be. A missing segment group is denoted by identifying the first segment in the group as missing.