You can edit any comment you've made, but not if someone else has subsequently commented on that comment. This keeps things on the straight and narrow.

So I'll try and be more accurate if I can. I never spot anybody else's mistakes and they don't matter anyway, although I always feel compelled to correct my own. I just don't like giving the impression that a new comment has been posted by updating.

to the down arrows - did Bargepole miss something ?