The device measures the amount of carbon dioxide in dry air, and expresses the result as number of molecules per million, usually called parts per million. (slate.com)
And this is very, very important to chemistry because chemistry has traditionally been about studying a large number of molecules and the effect that they have. (scientificamerican.com)
The device measures the number of alcohol molecules it can «see» versus the total number of molecules in the sample, and then calculates a percentage. (coloradospringscriminallawblog.com)