One thing that comes up time and time again is that once you start navigating in a topic stream, jumping down to later replies, jumping back up to earlier replies…
… you lose track of where you were in the stream. You “lose your place”.
But Twitter has this great new feature which lets you jump to the top with a visible button (this is an implied shortcut on iOS, which has the “tap to jump to top” feature, but Android does not and getting to the top after scrolling down a lot is excruciating, or at least it was until this feature was introduced)
So what if, when you jumped in a topic, we kept track of your previous scroll position before you jumped and showed it above the progress bar like so:
Now, in this case “back” could be up or down, but it’s the place you were before you jumped.
(There is a far more complex discussion we could have about what “where I was” actually means, but I want to keep it simple, meaning your last position before you jumped anywhere. Jumping over and over does not change your original position you started from. Each jump does not track the previous jump position, only the original, first place you started before jumping at all.)