I am trying to understand the positioning logic for a scrollbar's thumb after the user clicks on the scrollbar's track. I'm surprised it's not as straight forward as I originally believed.
The expected scenario is what occurs when the distance to move is sufficiently small. The thumb centers itself over the clicked position on the track.
When dealing with larger distances - the thumb does not center itself. Instead, it only moves a fraction of the distance. If the clicking action is held then the scroll continues until the thumb covers the mouse's pointer, but no centering is attempted.
I'm wondering a few things:
Why was the functionality implemented like this? Is this better UX than simply navigating to the location the user indicated?
How is the fractional move determined? Is it consistent across scrollbar implementations?