Why does SpeedIndex have second as their unit?

[sefeng211]

Looks like starting from this commit, SpeedIndex is interpreted as a time, this feels weird and incorrect.

[soulgalore]

Hi @sefeng211 I think Speed Index always been ms/s see https://sites.google.com/a/webpagetest.org/docs/using-webpagetest/metrics/speed-index but there was a move a year ago or something where all tools started to show it instead of having it unit-less, see for example https://github.com/GoogleChrome/lighthouse/issues/6130

[gmierz]

Hi @soulgalore, I find that using seconds as the unit is a bit misleading given that *SI metrics actually have units of %complete * time which is likely why lighthouse is showing them as unitless now.

I think the webpagetest documentation is also misleading since speed index is calculated as the area under a curve which is not a time value. I would agree that it approximates a temporal value, but it isn't exactly a temporal value:

The Speed Index is the average time at which visible parts of the page are displayed.  It is expressed in milliseconds...

[soulgalore]

Yep I see your point, but I think you are wrong how other tools show them, see the Lighthouse link I posted and the screenshot from LightHouse:

I don't changing though, can we have something better than it unitless?

[soulgalore]

This isn't perfect but maybe we can leave it as is for now.