This read-only value reports the negotiated UMTS QoS residual bit error ratio - the rate of bit errors expected to remain in delivered data after error correction - actually agreed with the network. An administrator monitoring a cellular router uses it to verify whether the carrier accepted the requested tolerance for bit-level errors, which matters for applications sensitive to subtle data corruption. For example, if a SCADA or telemetry application requested a low residual BER and the negotiated value comes back higher, the admin knows the link may introduce more bit-level noise than the application expects.