This is the rn of the ComputeConn object, the short label for this connectivity record under its parent compute node. Since this is a single fixed child under each compute node, the rn's main practical use is confirming during a walk that a given row is indeed the connectivity record and not another sibling object under the same blade. Expect the rn to read the same fixed short label for every blade in the domain, since it's structural rather than per-instance.