Useless. I tried to check the air quality in the house, in the car, on the street, I expected it to show relatively stable readings. But after the countdown to zero finishes and the meter is supposed to take actual readings, the reading instead continues to drop to near zero, even in a smelly new car with the window closed on a hot summer's day. Trademark EXTECH, hence paid 4/5 star reviews ignored. Unfortunately, this product didn't live up to my lowest expectations.
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