Um... Why the down vote? "Terrell used a sensitive air-quality meter to demonstrate that one high-end HEPA system brought the particulate count in a dusty room

Um... Why the down vote? "Terrell used a sensitive air-quality meter to demonstrate that one high-end HEPA system brought the particulate count in a dusty room down to virtually zero. His homemade system brought the count down to about 10 percent of its former level."