All this goes to show that is never simple to perform any of these tests. Proving intention to deceive is another complete matter. Taking care of checking every possible source of error, and constrain it, is the only way to go, but with anything that requires to meassure air flow on the mix, the error bars can be huge.
The error bars can be as messy or clean as one cares to make them with air flow, and generally everything else. Half of the automobiles on the planet (billions) measure air flow with very high accuracy and precision every moment they are turned on.