Why do the formaldehyde readings from an air purifier differ from those of other testing devices?

"1. Minor Differences: It is completely normal for there to be slight variations between two different formaldehyde detectors. These differences typically do not indicate a malfunction in either device but are due to the inherent characteristics of consumer-grade sensor technology.
Just as thermometers from different brands may display slightly different temperatures, two different sensors rarely show exactly the same readings.
2. Significant Differences:
1) Check if the testing locations are consistent. Formaldehyde distribution varies: near wardrobes/wooden panels > room center > near windows/doorways. Higher temperatures increase formaldehyde readings, while airflow from ventilation lowers them. Other gases like perfume or alcohol may be mistaken for formaldehyde, leading to falsely elevated readings.
2) Duration of use: The longer the device has been in use, the greater the likelihood of baseline drift and reduced sensitivity.
3) Compare readings taken at the same location and height while the device is stationary to eliminate interference. Focus on the trend rather than fixating on individual readings.
4) If the discrepancy remains significant, send the device in for repair."