The Garmin 405 GPS watch is really cool. When running (and walking) with my friends, we use a 2/1 ratio, meaning we run for 2 minutes, then walk for 1 minute. So, I set my watch's interval timer to signal us to begin each alternating interval. At this ratio, which we only use for distance running, we can average about 12 min/mile. The watch has a built-in limit of 99 such intervals, and each interval is a coupled run and walk segment, so there is a limit of just under 300 minutes (99 intervals x 3 min/interval = 297 min), or about 5 hours.
So, never did I think that I could run for more than 5 hours. However, as our mileage has increased, we are soon approaching the limits of the watch. Next weekend we will be run/walking 21 miles, and at 12 min/mile, that comes out to be about 250 min. Okay, but we will continue to increase our mileage until we reach 27 miles. At 12 min/mile, this comes to 324 minutes or more, if we stop for a bathroom break.
I didn't want to buy a new watch, so I figured out how to increase the number of intervals far beyond the 99 that are built into the watch. If you have a Garmin Forerunner (probably any variety) and want to know how to do it, well, here are my instructions.
The approach I used is to set un a new workout from within the Garmin Connect website, then upload the workout to the watch. It was surprisingly easy to do. Step by step instructions: