Air quality (PM2.5)
Five European cities, measured at the same moment: London, Lisbon, Rome, Athens and Helsinki. Each point on this chart is the average of those five readings, and the spread between them is what tells you how much ordinary difference to expect. That is the whole trick — the five readings measure the noise, so the average can be judged against it. When the average moves further than the spread can explain, something happened to all of Europe at once, not to one city's sensor.
PM2.5 across five European cities — subgroup averages & ranges
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Written out in full, the moment the chart sees it. No statistics knowledge required.
Tick a rule off and its points, its shaded runs and its card below the chart go with it — nothing is refetched, so you are looking at the same readings judged by fewer rules. Change how the readings are grouped and watch the limits move. The readings never change — only how many of them go into one point, and therefore how much ordinary difference the chart has been shown. Only the setting marked (the real one) shows the limits that were locked at baseline and have never been recalculated since.
Data source: Open-Meteo. Air-quality data by Open-Meteo.com, licensed under CC BY 4.0. Based on the Copernicus Atmosphere Monitoring Service (CAMS) European air-quality forecast. SPC Visuals is not affiliated with Open-Meteo.
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https://spcvisuals.com/live/air-quality
<iframe src="https://spcvisuals.com/live/air-quality/embed" width="100%" height="440" style="border:0" title="Air quality (PM2.5) — live control chart"></iframe>
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X̄-R control chart of Air quality (PM2.5), drawn from Open-Meteo. Limits were computed once from the first 40 points and frozen; they are never recalculated from the visible window. How these charts are built →
https://spcvisuals.com/live/air-quality/card.png
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