Yoctopuce writes that ABC assumes a room returns to about 400 ppm every few days, and that a continuously occupied room should switch it off. Adafruit writes the same 400 ppm outdoor figure for field and automatic calibration. RevK recorded outdoor air at 430–560 ppm and questioned forcing that zero. Without an ABC on/off log and an outdoor comparison, no page here can call the instrument calibrated.
What ABC is assuming
Yoctopuce’s 2015 calibration note — written by a module vendor — says automatic baseline calibration assumes the room sees about 400 ppm every few days. That suits an office empty at night, or a bedroom empty all day. A room that is occupied around the clock, a food process that adds carbon dioxide, or a system that removes carbon dioxide, should have ABC disabled. The stricter zero in that article uses nitrogen or CO₂-free air at about 0.2 L/min for about two minutes. A walk outdoors, away from vehicles, for about one minute is the everyday manual baseline.
Adafruit’s SCD-30 page repeats a 400 ppm outdoor figure for forced recalibration and for automatic self-calibration, and it writes a wait of about five days of qualifying intervals. Geerling wrote that SenseAir S8 self-calibration took about two weeks, during which the reading could sit about 200 ppm high. Those waits belong to those authors and those modules.
Outdoor air is not always 400
RevK, writing from a British house, recorded outdoor carbon dioxide at 430–560 ppm and questioned both the forced 400 ppm outdoor zero and the habit of treating the week’s indoor minimum as 400 ppm. That outdoor band is his walk, on his days. It is not an AirMeasure UK transect, and it is not rewritten here as a national outdoor mean. These pages do not call 400 ppm “the outdoor value”.
What these pages do not call calibrated
These pages do not call an instrument calibrated. That word would need the instrument identity, whether ABC was on, an outdoor or cylinder comparison, and the timestamps. This publication has not made that record. The blank CSV includes an abc_enabled column so the switch is written down with the reading. An empty cell is not a completed calibration.
Sources and scope
Sources checked on 23 September 2026. Numbered references point to the original publishers. Their sample measurements are not AirMeasure UK measurements. Manufacturer, tutorial and official material is identified separately.
- Yoctopuce, How to calibrate a CO2 sensor? ↗1 May 2015. ABC assumes a room returns to about 400 ppm every few days. Suits an office empty at night, or a bedroom empty by day. Continuously occupied rooms, food-process carbon dioxide or carbon-dioxide removal should disable it. Manual baseline: outdoors, away from vehicles, about one minute, then trigger. A nitrogen or CO₂-free zero is a stricter method. The publisher sells USB modules.
- Adafruit Learn, Adafruit SCD-30 NDIR CO₂ ↗Tutorial stating the SCD-30 is NDIR true carbon dioxide: “Unlike the SGP30, this sensor isn’t approximating it from VOC.” Field recalibration needs a known concentration. Automatic self-calibration is written as needing regular exposure near 400 ppm, continuous power, and about seven qualifying intervals of at least 18 hours (about five days). Component retailer, repeating a manufacturer specification.
- RevK, Air quality and CO₂ levels ↗Adrian Kennard, 20 March 2019. British engineer’s home-office and bedroom logs. A closed 5 m × 5 m office rose from about 430 ppm at 09:00 to 1000 ppm after 14:00 with one occupant. Bedroom nights exceeded 1300 ppm. Outdoor air was written as 430–560 ppm. Those rooms are his. They are not AirMeasure UK measurements.
- RevK, Understanding CO₂ air quality better ↗Same author, 21 March 2019. Cooking sent particles “off the scale” and also raised carbon dioxide. A curtain-blocked window barely dropped the bedroom reading. The author questions treating a weekly minimum, or outdoor air, as a 400 ppm zero.
- Jeff Geerling, Monitoring my home’s air quality with AirGradient DIY ↗8 September 2021. Lists SenseAir S8, Plantower PMS5003 and SHT30. A basement office sat near 900 ppm with the vent open and passed 3000 ppm after hours with it closed. Case heat raised temperature and humidity. Automatic baseline calibration was written as needing about two weeks, during which carbon dioxide could read about 200 ppm high. Those figures are the author’s.
No instrument in this note has been tested or certified by this publication. Evidence policy · Corrections
Write the conditions beside the reading.
The CSV has column headings and one empty row. It contains no fabricated sample readings.
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