I'm sorry, but I don't understand what it's a histogram of.

Ah, sorry! Such an oversight! (You get so involved in a project you think it's all natural...)

The histograms are:

For Reddit, they are of a headline's votes, of a headline's number of comments, and of a comment's votes.

For Delicious, they are of the numbers of users that have bookmarked a link, or applied a tag.

For Digg, of a headline's diggs, of a headline's number of comments, and of a comment's diggs.

For Hacker News, of a headline's upvotes, of a headline's number of comments, and of a comment's upvotes.

For StackOverflow, of a question's views, of an answer's votes, of the number of users that have applied a tag, of a user's reputation score.

It's hopefully all obvious once you install the script.

Adding larger versions of the screenshots in a sec..

A histogram shows a distribution of values. This just looks like a bar graph. Still useful, but I don't see how it's a histogram.

Ah, I see, I didn't even know there was a difference, thanks for pointing it out. I've always like the word "bar graph" more (it's more transparent), so bar graphs they are now!

A histogram of votes/diggs/etc where each story title is a bar in the histogram. I didn't get it at first but if you look at the delicious pic you can see clearly how it works with the tags sidebar.

Really nice =)

Check it on http://news.ycombinator.com/best

It works on MetaFilter now! Also, comment backbars are now more accurate. Download the latest script for these changes http://userscripts.org/scripts/show/51281

Are all the histograms based on popularity, diggs, upvotes, etc? The thumbnails are too tiny to make out and they link to the site, not a larger picture.

Minor thing - it seems to have messed up the comment threading. Check it:

http://www.flickr.com/photos/hitesh/3618708763/

edit: here it is with 4 comments. check out the whacked-out indentation of the comments -- the nesting is all off:

http://www.flickr.com/photos/hitesh/3618714801/

Done! It was a simple fix for a thing I had changed last minute last night. I've updated the version of the script at Userscripts so please just delete and install the script again at http://userscripts.org/scripts/show/51281. Sorry for the bug!

They are somewhat off indeed. This ironically only seems to happen in this particular comment thread. I'll look into it right away, sorry and thanks for the bug report!

oh not a problem. seems to be ok on digg & reddit so far and now that I get it, its kinda nice to have ..

it does happen in others too I notice