May Chart, page-9830

I would ignore that sort of metric. The majority of "activity" comes from "off screen": in some cases, it takes 10 times the screen volume to chew through a chart point, and sometimes less. Perhaps a better measurement is to look at total screen volume +/-10% of the current price level (say, 1 cent up and 1 cent down), in which case you get 12,090,400 on the bid, and 12,071,044 on the offer. Ignore the out of market stuff further away than that (as, in the majority, 10% captures most day's trading, except when you have events/announcements).