How We Tell A Quiet Source From A Dead One

A source is heard when it produced something we read, not when it answered a request.

A source counts as heard when it produced something we read, not when it answered a request: a feed can reply successfully and say nothing at all for a week.

Answering

Answering means the source replied when we asked in the last twenty-four hours. Most instruments answer every time and report rarely, because the ground or the sky was quiet.

When a source has filed nothing

It says why: a continuous feed writes to the archive rather than to reports, an instrument may be reporting below the threshold we act on, and some are waiting on a credential or are refused by the publisher outright. Those are four different things and we will not call them all silence.

No percentages

We publish counts of sources and the time since each one last spoke, never a single health percentage: a seismometer and a wire desk are not comparable, and an average over them would describe neither.