The Interactive Advertising Bureau (IAB) yanked the wizard’s curtain wide open Monday when it announced new guidelines for counting ad impressions in broadband streams. Here’s the key paragraph from an article in Online Media Daily:

“A valid broadband ad impression may only be counted when an ad counter (logging server) receives and responds to an HTTP request for a tracking asset from a client,” the new guideline states. That means measurement should not occur when the buffer is initiated; rather, “measurement should occur when the ad itself begins to appear on the user’s browser, closest to the opportunity to see.”