This read-only PerfTotalCount reports the lowest noise margin value observed on the DSL port, noting that this is always 0 for IDSL ports since noise margin isn't a measurable parameter there, scoped to the running total for the current calendar day so far. Operationally, a low minimum noise margin means the line came dangerously close to losing sync at some point, an early warning sign before a line actually drops. For example, checking today's worst noise margin so far lets an admin see whether conditions have already dipped dangerously low today, even if the line hasn't dropped yet.