I bought this HCHO level checker at my house. The calibration process described in the manual does not correspond to the actual operation of the device. The calibration time described does not reflect the actual performance of the device (120 seconds over 200 seconds are reported). Even the first measured values after the calculation in fresh air showed slightly increased values (yellow). A second test at the same place returned zero (green LED). A retest in other areas also showed a zero level. So there is no way to know for sure if the device actually works. I decided to see if the TVOC readings would change with exposure to the source. I opened a can of paint and put a pad on it. He registered high VOC levels. So he at least captures that aspect. The system must have a higher level of calibration (possibly provide a test kit to check the calibration). I spent $15 and am still not sure if the HCHO levels are acceptable. I would have to buy a chemistry test kit to check it.
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