cmLoopHistID is a read-only integer uniquely identifying a completed loopback test record retained in the loopback history table, distinct from the identifiers used for tests currently in progress via cmLoopID. An administrator uses this to reference a specific past test when reviewing diagnostic history for a line. For example, when comparing today's test results against a similar test run last week, the operator would look up the earlier test's specific cmLoopHistID entry.