This read-write value, given in meters over a range of 0 to 64000, tells the interface's line build-out circuitry how long the physical DS3 or E3 cable run is, which the hardware uses to adjust its transmit signal accordingly. It only matters on interfaces that actually have configurable line build-out circuitry; on those without it, the setting has no effect. An installer running a DS3 line over roughly 150 meters of cable would set this object to 150 so the interface can compensate its drive strength for that distance.