VercatusField and lab performance measure different conditions
Search Console's Core Web Vitals report is built from Chrome UX Report field data (real Chrome users, a 28-day window, p75 per URL group), and omits URL groups without enough data. Google's guidance is that when both field and lab data exist, field data should drive priorities; lab runs from one machine are for diagnosing and comparing templates, and help reach users on slow devices and networks that field data under-represents.
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AGrade A: official documentation or a standard. A grade describes the provenance of the sources above; it is not a probability that a change will work. The effect basis says how the size of the effect is known: measured by a study, taken from an industry report, only documented without a size, or not quantified.
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