Bests & Worsts Reviews from Amazon

I have changed my rating from 1 star to 2 stars. I have determined that for the unit I have the PM2.5 readings are reasonably accurate. However, the inaccurate PM10 readings (as discussed below) are a major deficiency. This is one of those occasions when I wonder how the product gets such good ratings. The PM10 reading is always approximately 1.4 times the PM2.5 reading (as also noted by another reviewer). It varies from the 1.4 ratio very little. The readings I get (outdoors) with this meter are reasonably close to the local air quality values for PM2.5 but are WAY TOO LOW for PM10. The low PM10 value gives an AQI that is also very low. What is going on here? The accuracy of the temperature and humidity readings don't look all that great either. I wonder about the readings for the other parameters that I cannot check all that easily (HCHO and TVOC)! Update: I have had some rather unsatisfactory interaction with the seller. If I understand their chinglish they insist that there is a direct relationship between PM2.5 and PM10 as a ratio. That is not true. Note that there are no accuracy specifications for this device and when asked for accuracy information the seller cannot or will not provide it. It turns out that the recording feature only works for PM2.5 and HCHO. The recording feature does not work for PM10, TVOC or AQI. 2nd Update: I have now tested several of these so-called air quality meters and none seem to get the particulate readings right. This one does do a reasonably good job for PM2.5. I am still having a hard time determining if the HCHO/TVOC readings are accurate. The HCHO/TVOC readings for outdoors are somewhat lower than inside the house which does make sense. The accuracy of the temperature and humidity readings are not all that great.