How readings are collected
Each station measures on its own clock and sends what it has when the link is up.
A reading is a level, a flow and a temperature taken in the same second. Stations keep seven days of readings on board, so a short outage loses nothing. Each one is stored with the field taken_at, not the time it arrived.
Thresholds
A threshold belongs to one station and one measure. When a reading crosses it, the people on the list are told once, and again each hour if repeating is on. Thresholds are kept on the alerts page.
What counts as a crossing
- Two readings in a row beyond the threshold.
- A single reading more than ten percent beyond it.
- A station that has been silent for thirty minutes, as 08 Reed bank is now.
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