An impression is an ad that loaded on a page or in an app. But loaded does not mean seen. If the ad sits at the bottom of a long page and the person leaves before getting there, there was an impression and nobody saw it.
That is why there is a second measure: viewability.
The industry rule
The IAB, the association that sets digital advertising standards, counts a display ad as viewed when at least half of it was on screen for at least one continuous second.
It is not a perfect measure of attention, but it is the common standard that lets you compare networks, sites and campaigns with the same ruler.
Why it matters
- For advertisers, a campaign with many impressions and low viewability is paying for ads nobody saw.
- For site owners, well-placed spaces that people actually see are worth more. Knowing the viewability of each space helps you choose where ads go.
- For both, viewability measured the same way avoids arguments about what was delivered.
How adPluga measures it
- Measurement happens on the device itself, in the browser or the app, through the SDKs and the tag.
- The "viewed" event is sent separately from the impression. That way one does not contaminate the other: there can be an impression without a view, but never a view without an impression.
- Each event is signed and counts only once, like any other event.
- On direct deals, viewability shows next to impressions, clicks and conversions, so both sides see the same number.
What you can do with it
If you advertise:
- compare your campaigns' viewability across sites and spaces, not just the number of impressions;
- be wary of large volumes with very low viewability.
If you run a site:
- put spaces where people actually look, close to the content and above the fold;
- avoid filling the bottom of the page with ads almost nobody sees.
Viewability tells you whether the ad was seen. Before that, you need to know the viewer was a person: see what invalid traffic is and why you should not pay for it.