Thanks for the info Lazy... I have a couple of air filters, so building my own is a no requirement, however, the air quality meters did get my attention.  Maybe with a meter, I might get that kick up my rrrs to actually turn my filters on.

What are they actually called and what obviously differentiates a good one from bad... other than exorbitant cost... Any hints a a good reliable one. 

If your first cut is too short... Take the second cut from the longer end... LBD