Karen said,

August 20, 2007 @ 9:05 pm

This is based on an old, old flowchart from at least the 1980s. I used to work as a lab technician, and we passed around a many-times xeroxed copy of the “Bad Column Flowchart” for chromatography columns. Much older than the Internet, and much cleaner (“Did you mess with it? You idiot!”).