Advertising: how we measure

What we count

• Viewable impression: at least half of the ad stayed on screen for one continuous second, in a tab in the foreground, after a sign of a human reader on the page (scroll, mouse, touch or key). One impression at most per ad slot and per page view.
• Ad loaded: the ad was sent to a page. A loaded ad that the reader never scrolls to is not a viewable impression.
• Click: counted once per link, within 2 hours of the page view. A later click still takes the reader to the advertiser, but is not counted.

What we filter out

• Known robots, crawlers, link previews, performance tools and scripted clients: they receive no ad and are never counted.
• Abnormal volumes: beyond 60 pages, 120 impressions or 20 clicks per minute from one network address, nothing more is counted.
• Each impression and each click carries a signed, single-use token: a forged, replayed or late token (more than 30 minutes for an impression) is not counted.
• Members of the Nofi team who are signed in are not counted.
• Every request that is not counted is recorded as a daily total, by reason, so that the filters can be checked.

What we do not collect

• No advertising cookie and no visitor identifier. No IP address is stored: rate limiting uses a keyed fingerprint of the address, kept for a few minutes.
• Reports only contain daily totals per ad, zone, placement, language and device type.

Known limits

• No filter is perfect: a robot that runs the page, passes for an ordinary browser and imitates a human gesture can be counted. Rate limits cap its effect.
• Several readers sharing one network address (common with mobile operators) share the same rate limit.
• Country is read from our network provider (Cloudflare); readers whose country is unknown are counted in the “World” zone.