Do you trust your GPS?

Superman and I each have a GPS application - his a Droid app and mine an iPhone app. You would think all GPS would measure the same distance as, well, the same. Mine mapped my last race at exactly the length it was supposed to be, though half marathoners complained theirs was long (I found out later some kids had moved the signs around. Race directors were able to fix them, but maybe not as precisely as they'd hoped).

After our last few long runs, I have developed a complete lack of faith in Superman's GPS. At one point it said we managed a 3 minute mile. Is that even possible? Certainly not for me! Our runs are peppered with me commenting "Is that your GPS? How fast are we zooming?" followed a short while later by "Mine just said mile ___."

After I posted about Saturday's long run, I wondered about our splits. While I do trust my GPS more than Superman's, I do not believe it 100% either. I was curious to see what Superman's splits said, and how they compared. Here's what our respective GPS showed:

You can see we're both all over the place. Sometimes his shows faster miles than mine. Sometimes my miles are faster than his. His splits have nothing to do with his announcements, either. Both our GPS announced mile 1 at the same time.

The biggest surprise for me was how fast we both measured the first 3 miles. The first half of this run is primarily uphill. My standard long run pace is somewhere between 12:30 and 13:00. No wonder I crashed!

For fun, I mapped things out on Veloroutes.org.

The first 3 miles

You can understand my confusion. It makes sense to me that Superman's GPS shows mile 3 as the fastest, considering more than half of it was downhill. On the other hand, by mile 3 I was already tired. A (comparatively) slower mile as shown on my GPS also makes sense. After that it just gets confusing. There's no way we did a 12:28 in mile 8. I quit running after mile 7, and on a good day I'm running a 12:28... on a short run!

Here's what the whole run looked like:

The full 11 miles

It also occurred to me after Saturday's post that I only took 2 Gu. This may have contributed to the "might not make it home" feeling. Either way, it was a calamity of errors I can't afford to make in the weeks to come.

What GPS do you use? Do you trust it?