This other chart shows that it only takes 20 grams of dust to cause 1 inch pressure drop.
http://www.aempower.com/files/dryflo...eabusetest.pdf
60 grams of dust is what caused 1 inch in the chart which I referenced in my previous post.
Confused...
OK I guess 20 grams of dirt loss after cleaning (versus dirty weight) is my new target air filter cleaning interval....