Sensor calibration
Correct a sensor that reads consistently high or low, and filter out spikes, without touching your hardware.
Calibration corrects a sensor that reads consistently wrong, before the reading is stored. Open Setup → Calibration in your site's dashboard. With more than one station, pick the station first: each is calibrated separately.
How a correction works
Each reading becomes:
corrected = raw x multiplier + offset- Offset shifts every reading by a fixed amount, for sensors that read consistently high or low.
- Multiplier scales every reading, for sensors that mis-scale. A rain
gauge catching 4% too little needs a multiplier of
1.04.
Leave a field blank to change nothing. Offsets are typed in your site's units, for example °F and inHg on an imperial site.
| Sensor | Correction |
|---|---|
| Outdoor temperature and humidity | Offset |
| Pressure (sea level) and pressure (station) | Offset |
| Indoor temperature and humidity | Offset |
| Wind direction | Offset, in degrees |
| Wind speed and wind gust | Multiplier |
| Rainfall | Multiplier |
| Solar radiation and UV index | Multiplier |
Dew point, heat index, wind chill, humidex, apparent temperature and cloud base are recalculated from the corrected readings, so they stay consistent.
Finding the right numbers
- Temperature: compare with a reference thermometer in a shielded, ventilated spot, over a full day.
- Pressure: compare with a nearby official station or an airport METAR at the same minute. It is the most commonly mis-set sensor.
- Humidity: ageing sensors usually read low. A saturated salt solution in a sealed jar reads 75%.
- Rainfall: pour a measured volume slowly through the funnel. The multiplier is what you poured divided by what was recorded.
A large correction usually means something else is wrong, such as a sensor in direct sun or a blocked funnel. Fix the siting first.
Spike limits
A spike limit is the largest change accepted between two consecutive readings. Radio interference, a dying battery or a loose connector produce single readings that jump further than any weather can. A reading that fails its limit is dropped, as if the station never sent it.
- Temperature, humidity, pressure, wind speed and wind gust limits cap the change between readings.
- The two rain limits cap the rain rate and the rainfall in a single reading outright, because a phantom bucket tip has no previous value to compare with.
- Readings more than an hour apart are never compared, so a gateway coming back after a quiet night is not mistaken for a spike.
Keep limits generous. A real cold front can move the temperature several degrees in minutes, and a limit that is too tight deletes real weather. The Spike limits tab shows when a reading was last rejected and which one; raise the limit if that happens on calm days. The "A reading was rejected as a spike" alert tells you when it happens.
What calibration does not change
- Stored history. A correction applies to new readings. On a WeatherLink station roughly the last hour is also re-fetched and re-saved with it. Older readings keep their values, so charts show a small step when you save. To fix stored readings, use the data editor.
- Imported history. Files imported from weewx, CumulusMX or CSV are stored as they are.
Everything else, your public site, charts, records and CSV export, reads the same corrected archive.