This read-only value, in microseconds, reports the round trip delay measured during the last non-destructive loopback test on this endpoint, applicable only for that test mode. An admin uses this measured delay to assess actual path latency for the connection, providing concrete data for capacity planning or diagnosing unexpectedly slow application performance over the ATM circuit. For example, if applications running over an SPVC seem sluggish, the admin can run a non-destructive loopback test and then read this object to get a hard measurement of round-trip delay confirming or ruling out the network path as the cause.