Just to be sure this meter actually reads anything I ran an experiment with it. It did detect rising CO2 levels in a closed container with a burning candle as it should have. Would I trust actual values in parts per million from what I read on the meter? Probably not, it is a 36 dollar meter, but I would trust it way more than my senses to detect levels for CO2 and HCHO and TVOC. One word of caution is the meter is not instantaneous, it takes a couple minutes to warm up and the mean-values given for CO2 and HCHO and TVOC are updated at different time intervals, 10 minutes for the CO2 and 60 minutes intervals for the HCHO ( Formaldehyde ) and 30 minute intervals for the TVOC (Total Volatile Organic Compounds). The instructions say not to have a lot of faith in the real-time measurements of CO2 and HCHO and TVOC ( Those values fluctuate up and down, especially for CO2) but be more trusting in the 'mean-values' for these which is displayed directly below the 'real-time' measurement on the meter's display. At the bottom of the meter's display is a grid of 6 boxes for an overall assessment of air quality. A green box means good air quality, a yellow box means the air quality is not so good and if you see your air quality in the red box you should have concerns, maybe break open a few windows and figure out if your furnace, or water heater are working and venting properly, or maybe an oven has been left on too long. The meter is made in China so hard to know how much faith you should put into their air quality assessments put together at the factory that made the meter. I am sure nothing here is OSHA approved, just better than winging a guess. For 36 dollars it is not a bad investment, at least in my opinion. I do see a 3 fold rise in the CO2 levels for my apartment when I put pizzas in the oven here and run the oven for 20 minutes, but after I turn the oven off the CO2 level goes back to about 600 PPM which according to the table given by the manufacturer of the meter is good air quality.
