I suppose that makes the system about 90% accurate, and for a non-competitive slug like me perhaps absolute accuracy is not essential. Still, today I was disappointed when the Nike+ announced the end of my run was 5.99 miles in a time of 1:02, with an average mile pace of 10:29. In reality, at 1:02 for 6.2 miles I achieved very close to a ten-minute mile average pace, which is my current goal.
From what I have observed, the Nike+ records distances as being shorter when the running pace is consistent, and longer when the pace varies throughout the workout.
