Athletes: Write Your Own Apps for Your GPS Watch
You can in fact do that, but it'll cost you. I don't know anyone who has a $500 Sunnto Ambit GPS watch, but the latest version includes access to an "app store" where you can download and install apps such as predicting your marathon time or counting your hill repeats. The former uses your current pace and the distance yet to be run to estimate your finish time. You can even see the formula. The latter has you click a button at the top and from there on it counts how many times you reach that location. I'm guessing it's based on altitude, from the graphic.
Even more intrguing for the geeky athlete is a web-based tool to build your own app. Based on the apps above, I'm guessing it's a lot like write a formula in Excel and optionally, attaching an action to it, such as clicking a button or causing a beep for an alam.
It's an interesting idea, but the more I run (both in years and the distance I cover) the less tech I prefer. My constant companion these days is a Timex Ironman 100 lap count TAP watch. I love that (1) it can count 100 laps (for those looonnnngggg races), (2) I can stop a lap by tapping the face of the watch (no button pushing) and (3) the Indiglo mode that when "on" lights up the screen on every tap. I use the Indiglo mode regularly during fall outdoor evening track, when we run literally in the dark.