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 full previous calendar day's totals for the DSL port. 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, an admin checking yesterday's worst noise margin reading can tell whether a line that's failing today was already showing warning signs the day before.