The part of this I always forget is how lazily the ranking is applied. HN does not rescore the list on every page load. A story is rescored when someone upvotes it, and separately one story out of the top 50 gets picked at random every thirty seconds and rescored. Pages cache for another ninety seconds on top of that.

So the front page is never a clean rendering of the formula. A story that stops getting votes can sit at the wrong position for minutes at a time.

Which is also why the penalty figures in the post are ranges rather than numbers. Shirriff is inferring them from stories ranked lower than their raw score implies, and a story that simply has not been rescored recently looks exactly the same from outside. He lists that as one of his sources of error, along with neighboring stories carrying their own penalties.