Readings
How metrd records and stores readings.
Every value metrd shows you - a watt figure on the live display, a state of charge percentage, a forecast slot - comes from a reading. A reading is a single measurement from an integration at a point in time, tied to whichever device on that integration it came from (your solar array, your battery, and so on).
Metrics
Each device reports a set of metrics depending on what it's capable of measuring. Common ones include:
| Metric | Typical unit |
|---|---|
| Battery state of charge | % |
| Battery charge / discharge rate | W |
| Solar (PV) output | W |
| Inverter AC output | W |
| House load | W |
| Grid import / export | W |
| Battery / inverter voltage | V |
| Battery / inverter current | A |
| Battery / inverter temperature | °C |
| Grid frequency | Hz |
Not every device reports every metric - a solar array reports PV output but not state of charge; a grid-tie inverter without a battery won't report charge rate at all.
Live vs. historical vs. forecast
A reading is tagged with the capability it came from:
- Live readings reflect what's happening right now, and drive the display.
- Historical readings are past values, used for backfilling gaps.
- Forecast readings are predictions of future values, such as tomorrow's expected solar generation.
Retention
Keeping every raw reading forever isn't practical, so older readings are bucketed - averaged down into coarser time intervals the further back they go. Recent data stays at full resolution; older data is progressively compressed. This keeps history useful for trends without the storage cost of keeping every single point indefinitely.