Product review (5 stars): Outside our air was good, inside it was poor
I can't gauge the accuracy of the measurement of this meter, but it works exactly as one would expect. I tested it in several scenarios. Outside our air was good, inside it was poor. After some adjustments to our HVAC system (our builder originally had a hole in our return air duct to draw in fresh air which I taped over since it made the air conditioner work very hard in the summer ... I took the tape off this), the inside air changed to  a 'normal' rating by the meter. I then found that by turning the fan on the HVAC system from 'auto' to 'on' so that it runs continuously, we got a 'good' rating.