I don't know if it was done before, couldn't find anything like that, so I made a tiny script that sums all mertis of a post and displays it before individual merits
Like this:

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Thank you. Your userscript is useful, sure. I think other users will like it, of course if they are fan of userscripts, too. Like this thread, I do have to count total received merits of threads by myself, manually. With this script, people can naturally get it.
How about that one?
@small improvement request. In merited posts, show your name in red or bold or..You can read some ideas in that thread: Glow, Highlight, dropdown list.
It will be great if you can make an userscript for that demand.
You made it!theymos answered there:
Pretty sure it's first by merit awarded for that post (obviously), then by activity.
Right. And in case of equal activity, member ID is the tiebreaker.
Added newest userscript.