How does attention span measurement work?
There are many different methodologies of attention measurement being employed across the industry. The first is gaze-based methodologies which focus on having an element of real, human eye-gaze data to track attention.
The second group are non-gaze based methodologies that rely on other metrics - often referred to as proxy metrics for being used in place of actual attention - and historical data or norms, to extrapolate an estimation of attention paid to an ad.