The Chrome User Experience Report (CrUX) provides real user experience data on millions of websites, focusing on key user experience metrics such as loading performance, interactivity, and visual stability. Core web vitals include metrics like Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift, which are essential for a positive user experience and are ultimately tracked across various Google tools. PageSpeed Insights (PSI) leverages CrUX data and performs analysis via lighthouse to report on web performance, offering insights and suggestions for improvements.

1. CrUX Report/Web Vitals
The Chrome UX Report (informally known as CrUX) is a public dataset of real user
experience data on millions of websites. The Chrome User Experience Report is
powered by real user measurement of key user experience metrics across the public
web, aggregated from users who have opted-in to syncing their browsing history, have
not set up a Sync passphrase, and have usage statistic reporting enabled. The
resulting data is made available via:
1. PageSpeed Insights
2. Public Google BigQuery Project
3. CrUX Dashboard on Google Data Studio
4. CrUX API
The data in the Chrome UX Report is a 28-day rolling average of aggregated metrics.
This means that the data presented in the Chrome UX Report at any given time is
actually data for the past 28 days aggregated together.
Web Vitals/Core Web Vitals
Web Vitals is an initiative by Google to provide unified guidance for quality signals that
are essential to delivering a great user experience on the web. Core Web Vitals are the
subset of Web Vitals that apply to all web pages, should be measured by all site
owners, and will be surfaced across all Google tools. The metrics that make up Core
Web Vitals will evolve over time. The current set for 2020 focuses on three aspects of
the user experience—loading, interactivity, and visual stability—and includes the
following metrics (and their respective thresholds):
1. Largest Contentful Paint (LCP): measures loading performance. To provide a
good user experience, LCP should occur within 2.5 seconds of when the page
first starts loading.
2. First Input Delay (FID): measures interactivity. To provide a good user
experience, pages should have a FID of less than 100 milliseconds.
3. Cumulative Layout Shift (CLS): measures visual stability. To provide a good
user experience, pages should maintain a CLS of less than 0.1.
For each of the above metrics, to ensure you're hitting the recommended target for
most of your users, a good threshold to measure is the 75th percentile of page loads,
segmented across mobile and desktop devices. Tools that assess Core Web Vitals
compliance should consider a page passing if it meets the recommended targets at the
75th percentile for all of the above three metrics.

2. About PageSpeed Insights
PageSpeed Insights (PSI) reports on the performance of a page on both mobile and
desktop devices, and provides suggestions on how that page may be improved. PSI
provides both field and lab data about a page.
Field Data
When PSI is given a URL, it will look it up in the Chrome User Experience Report
(CrUX) dataset. If available, PSI reports the First Contentful Paint (FCP), First Input
Delay (FID), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS) metric
data for the origin and potentially the specific page URL.
PSI reports the 75th percentile for all metrics. The 75th percentile is selected so that
developers can understand the most frustrating user experiences on their site. These
field metric values are classified as good/needs improvement/poor by applying the
same thresholds shown above.
Lab Data
PSI uses Lighthouse to analyze the given URL, generating a performance score that
estimates the page's performance on different metrics
How the Performance score is weighted
The Performance score is a weighted average of the metric scores. Naturally, more
heavily weighted metrics have a bigger effect on your overall Performance score.
Lighthouse v6
Explore scoring with the Lighthouse scoring calculator
https://googlechrome.github.io/lighthouse/scorecalc/
Serial No Audit Reference Weight
1 First Contentful Paint https://web.dev/fcp/ 15%
2 Speed Index https://web.dev/speed-index/ 15%
3 Largest Contentful Paint https://web.dev/lcp/ 25%
4 Time to Interactive https://web.dev/tti/ 15%
5 Total Blocking Time https://web.dev/tbt/ 25%
6 Cumulative Layout Shift https://web.dev/cls/ 5%

3. References
https://developers.google.com/web/tools/chrome-user-experience-report
https://web.dev/chrome-ux-report/
https://web.dev/vitals/
https://developers.google.com/speed/docs/insights/v5/about