PR, I believe, is "personal record". If you click into them, then I suspect that it'll show you over which segment...
Ah yes, that makes sense too.
I can't quite figure out what personal records are (I think I have 6 of them). I mean, it sounds obvious doesn't it? But I'm darned if I can figure out how they're worked out. I'm sure it's in the FAQ somewhere but who reads those?
What it does seem to be good for is extracting sections and getting stats where you forgot too press 'lap'. 
