Quick Nike+ Question?

Hmmmm not not sure how you get a big picture! But you get the idea - this is my graph this morning, now see that big dip down? How does that happen, I know for sure I didn't run a 10min km there - I was running a good pace the whole run. Any idea why that happens? Just about every run I get a huge dip somewhere on the graph that doesn't make sense.

Oh BTW, I don't really run that fast - it was actually about 12.1km, I STILL haven't got around to calabrating it properly, I've got used to adding about 10sec to each per km total!