The duration is reported by the listener under the same conditions as in ``DB'', above. The duration represents the time-of-flight of the ultrasonic pulse, compensating for the various time offsets for accuracy. This value can be used to calculate a distance with with more precision then the DB distance, because the latter uses a (temperature-compensated) value for the speed of sound, which may introduce some error. For example, to determine which of multiple beacons is closest to the listener, compare the DR values. The units of the reported duration is microseconds.