XCode 5: What does the blue line in memory tab stand for?

Question

What does the blue line in the memory tab gauge represent?

Answer 1

IIRC, It represents the range of the last few minutes of memory utilisation in Memory gauge and CPU utilisation in CPU gauge. So, you know whether things have been wildly swinging back and forth or is it just been picked at a narrow range.

Here in your case, 43MB is what currently being utilised but the inner blue arc represents the range of memory utilised by your app over a certain period. For example, CPU is utilised in the range of 60% -100% and memory is 30-120MB.