Page Speed Insights shows CLS 0,17 even though it is 0

[Markus Kirchler]

Hi, why do i get CLS 0,17 on Computer for this site 

https://www.graber-partner.com/de/lexikon/22-irpef-imposta-sul-reddito-delle-persone-fisiche.html even though the report shows 0 ?

https://pagespeed.web.dev/report?utm_source=psi&utm_medium=redirect&url=https%3A%2F%2Fwww.graber-partner.com%2Fde%2Flexikon%2F22-irpef-imposta-sul-reddito-delle-persone-fisiche.html&hl=de&form_factor=desktop

[Barry Pollard]

The report shows 0,17 for CrUX data - which is measured by real Chrome users using that page (known as "field data"). This is in the "So sieht die Leistung auf der Nutzerseite aus" section.

The lab test ("Leistungsprobleme diagnostizieren") which does a simple load of the page without any interaction shows a CLS of 0.

So the CrUX field data at the top, can be different to the lab data shown below if any interaction (scrolling, clicking, hovering...etc.) with the page causes CLS.

For example, I notice for that page, if you scroll to the bottom, the ProvenExpert reviews in the footer shift the logos to the right after it loads causing a small CLS shift.

What's perhaps more important, is that there is not enough field data available for this page, so PSI has instead given you the CLS score for the whole origin:

This means that even if this page has no CLS (other than the small one I have noted in the footer), other pages on this site, which have CLS, will be contribute to this 0,17 score.

Finally the field data at the top is taken over 28-days so if you have recently fixed CLS issues it will still show a CLS value here for a number of days until enough page views on the fixed pages are see.

These articles should give more information to help you understands this.

• Using the Chrome UX Report on PageSpeed Insights - note we're in the middle of updating this to show the latest changes to PSI so the screenshots are currently of the old version.
  
• Why lab and field data can be different (and what to do about it)
  
• Debug Web Vitals in the field
• Core Web Vitals workflows with Google tools
  

Barry

[Markus Kirchler]

Hi Barry, thanks for this very good response, this makes it much clearer to me! Thx!