In the documentation that defines Speed Index (https://sites.google.com/a/webpagetest.org/docs/using-webpagetest/metrics/speed-index), there is a section called “Visual Progress from Paint Events”. This section of defines an alternative definition of Speed Index, that is described as more lightweight and does not require video capture.
I would like to know: If I have a private WPT instance, is it possible for me to run tests with this alternative definition of Speed Index? If so, what settings/code do I need to change?
I have a couple of secondary questions:
-
Where in the source code can I find the precise definition of the paint-event based speed index? I would like to know more about what kind of “filtering and weighting” gets used to compute the final score.
-
Has anyone compared the “consistency” of the original speed index and the paint-event based one? What I mean is: If I do N consecutive runs for a particular browser and website, how similar will my N speed index measurements be?
My apologies if these questions have really obvious answers — I’m quite new to the tools WPT provides.