Sometimes it is very easy to find the changes. Weather can effect this BUT you can stuill get an idea, also the first 100 or so miles it after the filter or filter system is installed (your engine) is pulling excess oil ( I alwats use the clean and re-oil type, have never used the replace it type ( that one of the reasons for the K&N Style-gauze NOT PAPER filters in the first place- As the moisture in the air (even perfectly clean air) will cause the pores of the paper style to close restricting flow. Which is the reason those type have a mileage change interval. Remember DIRT does NOT block off air flow like closed pores do! If it did insects,animals, etc. that live in the ground could not breathe. Ask anyone who rides or races on ANY type of vehicle on dirt why it is the FILTER ALWAYS USED. No matter the ENGINE CAN BREATHE. Anyway before you install Find a nice diner a 100 of so miles away, take your spouse to breakfast - LET THE VEHICLE DO THE WORK - think cruise control (the computer will help eliminate throttle application variances. Install your filter, go the 100 so so miles. Then BREAKFAST TRIP again.
Why when you get a boo-boo due Doctors wrap that boo-boo in gauze? Maybe because it allows the air to get to the skin anf FILTER ALL the bad things that they do NOT want getting to that boo-boo. If you wrapped that boo-boo with duct tape. paper etc. it would for sure be a much better "filter" as far as restriction is concerned but the good stuff "air" would not get to where it is needed. So in a test do you actually want the best filtration? Or the PROPER amount of Filtration? Take a paper towel cover your mouth, you can still beathe, spray a mist of water on it, NOT SO MUCH. Take a piece of gauze bandage from your medicine cabinet preform the same test.