That is the question. I have a Nike Plus attachment for my iPod Nano. It wasn't anything I really planned on purchasing, but I ended up with a $50 gift card for the Nike store, and since I don't run in Nike, this is what I came up with to buy (that and a sports watch). I started using it in April. I read some reviews about it and people were pretty happy except for a few thought the mileage was a little off. I was on the fence. I run about 4 miles around my little neighborhood (one small loop = 1/2mi, one large loop = 3/4 mi). I think I start and stop at the same place everyday and it tells me something different everyday... one day with be 4.09 miles and the next day will be 4.15 miles. One day it was even 3.99 miles. I thought I had finally decided to believe it at the Labor Day race when I wore it and it measured the 8 mile course as 8.08 miles. I thought that was pretty accurate and decided to believe what it was telling me.
Until this morning.
Remember, I have a 10 mile race coming up in less than a month? It's still 103ºF out here with no relief in sight. I have a volunteer commitment in the morning for which I have to get up at 4:30am and it won't be over until 7:30am. I really don't want to run in the heat after that. My choice today was to squeeze in 5 miles instead of getting through my normal 4. I thought tacking on 2 more small neighborhood loops to my 4 mile course would easily make 5 miles. When I finished it told me that I had run 4.85 miles. This did not make my day.
So do I believe this gadget or not? Is it one of those things you believe when it is convenient to do so and ignore it when it isn't? Do I believe I ran 5 miles this morning? Or did I need to run by a few more houses to make sure of it?