It tells you not only the post number, but also the total posts in the thread. For example, it would show 5/7 if you were on the 5th post or a 7-post thread. Useful, except that It uses the post on the top of the page for the number. But people generally only scroll once they’ve read at least half the page. I think it should use the bottom-most post, so that the reader knows there are more posts. Otherwise, it forces you to think there are more posts below, when there actually are not. This takes away from the enjoyment of a good thread ever-so-slightly.
Mods: please feel free to move this to Great Debates if it gets out of hand.
I just grab the slider and drag it to the bottom to see the total number of posts. Then I go back to where I was.
Maybe we are seeing different views, but the bar I see already shows how many posts there are in the thread. That was kind of my point. When I see 5/7, it is telling me that I am on post 5 out of 7 total. However, I can already read post 7 (in most cases with average length posts) because it’s on my screen. So I naturally think that there are still 2 more posts below what appears on my screen, even if there are not. I think that the very last visible post should be the post number shown.
Isn’t that really your problem rather than the system’s problem?
Is there a way to quickly skip to the very top or very bottom of a thread? Especially on mobile, scrolling can take a long time.
Tap on the numbers on the bottom right. (5/162 or whatever) Then swipe the scroll bar to the very top or bottom.
Perhaps. That’s what I’m trying to find out.
Absolutely not. How do you think a few billion people in the IT industry would make a living if everybody had that kind of attitude?
I’ve been in the IT industry. It’s always the users’ problem. Been that way since the first cup holder was built in.
At the very top of the bar is the date when the OP was posted. Click (or tap) on it to go to the first post. Similarly, at the bottom of the bar there’s a date or time when the thread was last posted. Click (or tap) on it to go to the latest post.
Dude, it was called a ‘CD-ROM Drive.’
As for the OP, I actually agree. It feels a little glitchy. With my window size, it’s pretty consistently off-by-two. That said, I barely care. If I were a software dev or pm or whatever on Discourse, this would be pretty much the lowest severity item I could create. I know the thread is over when I scroll down, and I start seeing the ‘Share’ and ‘Bookmark’ buttons rather than more posts. It’s a pretty good indicator.
While in the topic:
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Tap the title of the topic to jump to the top of the topic.
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Tap the top or bottom dates on the vertical timeline to jump to the top or bottom.
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Press ? to see a list of keyboard shortcuts and as you would expect, home takes you to the top and end takes you to the bottom.
From the topic list:
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To enter a topic at the top or bottom, tap the reply count in the topic list in the Replies column
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To enter the topic at the bottom, tap the last reply time indicator in the Activity column
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Tapping the topic title will put you in the topic at your last reading position (the bottom-most reading position, we don’t track “reading holes” because down this path lies madness 
)
This and much more is covered in Discourse New User Tips and Tricks
Also as an aside, post numbers can get a little weird if there are whispers (staff asides), post deletions, or small post actions (topic split, topic open, topic closed) posts in there. Don’t expect a 1-to-1 relationship between visible posts and the post number.
If it’s an exceptionally long thread, trying to scroll down I keep getting stymied by the infinity wheel. Usually now, I just give up trying to read the entire thread and use the sliding bar on the right to tap the most recent post and maybe look at the last few above it.