#### PerformanceNewsletter
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#### Issue 46
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#### Editor’s Note
Performance work relies on metrics—a predefined set of calculations that are supposed to, in some way, quantify the aspects of user experience.
Without metrics and their trends, we are in the dark. But metrics are tricky—some of them are no longer relevant, all of them are contextual, some can be hard to interpret, all of them can be unstable in monitoring and even more so; the recommendations keep shifting.
It’s necessary to pay attention to what matters to both your context and the progression of the platform.
Stay informed and act accordingly.
— Karolina
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#### article
## Consider the environmental impact of your code
[Danny van Kooten](https://twitter.com/dannyvankooten/) puts the necessary perspective on the environmental cost of *more* code. Did you know that shaving off a single kilobyte in a file that is being loaded on 2 million websites reduces CO2 emissions by the same amount as 5 flights from Amsterdam to New York? Blimey.
[]() CO2 emissions on the web →
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#### article
## Know how your Performance Score will change
Lighthouse, the open source performance and quality testing suite is gearing up for 6.0 release. We outlined the most significant changes, including the revamped Performance Scoring algorithm. Your score will be calculated differently—based on a new generation of metrics with different weighting.
[]()[Lighthouse Changes How Performance Score is Calculated →](https://calibreapp.com/blog/lighthouse-changes-scoring-algorithm)
#### talk
## Understand the difference between metrics
[Ire Aderinokun](https://twitter.com/ireaderinokun) gave a great talk at last weeks’ remote edition of [Perf Matters conference](https://perfmattersconf.com/). In her presentation, Ire outlines critical performance metrics, the difference between them, as well as when they are relevant to use—a comprehensive primer on metrics, including the newest additions to the testing repertoire.
[]()[FMP, TTI, WTF? Making Sense of Web Performance →](https://noti.st/ire/556Xk1/fmp-tti-wtf-making-sense-of-web-performance)
#### tools
## See how metrics change as you browse the web
[Dion Almaer](https://twitter.com/dalmaer), who works on Google Chrome and DevTools, created a handful of Chrome extensions for live tracking key interactivity and user experience metrics as you browse the web. Each extension monitors one metric, covering Largest Contentful Paint, First Input Delay, Cumulative Layout Shift and First Contentful Paint.
[]()[Browsing the Web while watching it’s vitals →](https://blog.almaer.com/browsing-the-web-while-watching-its-vitals/)
#### talk
## Learn how Walmart approaches performance
In his talk, [Vasanth Krishnamoorthy](https://www.linkedin.com/in/vasanthkrishnamoorthy/) explains how Walmart went through their performance journey. Vasanth covers basic principles, actionable strategies that resulted in speed improvements and challenges ahead. Remember—performance is a journey, not a destination.
[]()[Turbocharging Walmart.com: Speed without compromise →](https://speakerdeck.com/vasa/turbocharging-walmart-dot-com-speed-without-compromise)
#### video
## Improve performance with IntersectionObserver
[Jeremy Wagner](https://twitter.com/malchata) started a new YouTube channel where he will be covering actionable strategies for making your sites and applications faster. In the first episode, Jeremy covers the IntersectionObserver API and how to make the most out of it in a performant way.
[]()[Hell-bent for Webperf: The IntersectionObserver API →](https://www.youtube.com/watch?v=3Esjyp7wnhQ)
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