5 miles?

I'm reading a book called The NonRunner's Marathon Trainer and they have a training schedule that I'm trying to follow. This past week I've followed the schedule of 3 miles, 4 miles, 3 miles....and then Sunday's run was supposed to be 5 miles! I went out for my run on Sunday morning and ran until my Nike+ watch said 5 miles. I was a little suspicious that I didn't actually run 5 miles because it didn't take me as long as I thought it would. I drove the route in my car and discovered that it was only 4.2 miles, not 5 miles. Although 4.2 miles is a good distance for me, I'm a little disappointed that my watch is off by so much! I need to calibrate it again and check it for accuracy more often.

This is a great book. It takes a conservative and safe approach to training. I'm finding it very helpful as I increase my mileage.
Today, is a day off. I'm going to look for a track where I can calibrate my watch!