This is the number of port errors, such as parity or framing errors, that must accumulate before a medium-severity alarm is generated, with a new alarm re-firing at each additional multiple of that threshold. Setting this to a specific count rather than a rate or percentage gives an admin a proportionate escalation pattern, repeated alarms as errors keep accumulating, useful for judging whether a noisy line is getting steadily worse versus a one-time burst. For example, with the threshold set to 10, as the description's own example states, an alarm fires at the 10th error, another at the 20th, another at the 30th, letting an admin gauge ongoing line severity by counting how many alarms have fired.