← Glossary · Measurement & Metrics Measurement & Metrics Definition varies Likelihood to See (LTS) A stricter measurement tier than OTS: people in the exposure zone while the screen is active and viewable. Measurement bodies (IAB, MRC) place it between OTS and audited audience impressions; exact criteria are still being standardized. Also known as: LTS Source: MRC OOH Measurement Standards Related terms Opportunity to See The probability of being exposed to a medium’s content or advertising. OTS does not require actual exposure to all content — it counts the chance to see, not confirmed viewing. Audience Impression The canonical DOOH measurement unit: the total number of people with an opportunity to see (traffic), adjusted for notice and dwell time and calibrated to the spot length. The same concept the industry also calls Visibility Adjusted Contact (VAC). Viewable Impression An impression that met a viewability condition (the ad was actually on-screen and seeable). The relationship to VAC/audience impression is debated — some bodies treat viewable impressions as a bottom-up counterpart to VAC’s top-down approach. See also Research Attention benchmarks across media