Every now and then I get a crazy idea. Most of the time I'm smart enough to ignore it, but sometimes, in a moment of insanity, I convince myself the idea is the best one I've ever had. Two months ago, that idea was to try and run 5km in under 20 minutes.

Unless you're an experienced runner, you don't just put on your running shoes, hop out the door, and run 5km in under 20 minutes. It takes time to train and condition your body to put up with the unfamiliar stress. Since the insanity took over, I've been training three times a week, gradually building up speed and stamina. I'm a very long way off, but my time is already down to 25 minutes.

I've been using my Garmin Forerunner 210 to record my progress. Like many gadgets it has a built in GPS receiver, allowing the watch