Engagement
Attention metric
Also called attention time.
Attention metric is a constructed measure of whether someone was actually looking, not just that the page loaded. It folds visibility, input and time into one score.
How it is measured
Vendors count seconds in which the tab is in front and the person scrolls, clicks or moves the pointer. Each vendor weights those signals differently, so scores from two tools cannot be compared. The output is usually seconds of attention per view or a percentile.
The simplest honest version uses things you can explain: seconds the tab was visible, and how far the page scrolled. Tarsier's engagement pings count visible seconds only, which is one ingredient, not a score.
Worked example
A publisher sells two ad slots on a long feature. Both load on every view. The top slot gets 14 seconds of attention per view and the slot near the footer gets 1.2 seconds, because 80 percent of readers never reach it.
An advertiser pays three times as much for the top slot. Standard impression counts for the two are identical, which is why the gap was invisible before.
How it differs
An attention metric tries to say whether someone looked. Engagement time counts only visible seconds. Scroll depth records how far the page moved. Viewability is an ad standard that asks whether pixels were on screen for a set time.
Common errors
Treating a score as fact when the formula is private. Comparing scores across vendors. Equating seconds with understanding. Collecting pointer data without a consent basis. Selling attention figures nobody else can reproduce.
In practice
If you have to report attention, use a measure you can explain in one sentence, such as visible seconds plus depth reached. Compare it only across pages of the same format.