A difference of 12-15 seconds isn't what I would call imperceptibly small, but then I'm probably a lot more conscious of my PBs than many runners.
I *wish* I were that perceptive! I imagine being able to feel that difference in distance or time would also translate into a really good feel for pace while running. Which would obviously be very helpful in the middle of a race. That is awesome.
PRs:
5k - 22:53 (May 2015)
10k - 50:00 (unofficial; part of 20k race, March 2015); 50:33 (official; July 2016)
HM - 1:48:40 (Apr. 2015)
I would annoy the crap out of you with the obsession, hair splitting attention I give to my PR's.
Arm warmer vs bare arm PRs!
I'll get right on that, thanks for the idea!