This is the current signal-to-noise margin this VDSL transceiver measures on its received signal, expressed in tenths of a decibel, indicating how much headroom exists above the minimum SNR needed to maintain the current connection reliably. It's one of the most important real-time health indicators for a DSL line, since a margin that's dropping toward zero predicts an imminent loss of sync or forced rate renegotiation even before the line actually drops. A value of 60 (6.0 dB) on a line configured with a 6 dB target margin is right at the edge of acceptable and worth monitoring closely, while a healthy line typically runs several dB above its target.