Before anyone asks, yes I did lots of research and searched well on this forum. I'm still thoroughly confused. All I see are either terrible explanations of single numbers ("Beta Ratio 2"), or formulas without explanation at all ("2/20=6/20"). All I know is my math teacher would have had a fit if I wrote 2/20=6/20. Can anyone help decipher WIX's information of these 2 filters. Everyone says they are interchangeable, but there are definitely some different numbers, therefore I don't think that's accurate. I do understand what both represent, and the principles of what they do, just looking to understand how to interpret the numbers. Edit: Also, what is this Nominal Micron Rating at the bottom?