Stop watch, Garmin, or something else just pick your poison when it comes to tracking your splits during a race. I hear people all the time talk about wanting to hit this split or that split during a race. I listen and then just smile. In my opinion too many people put way too much effort into worrying about their splits.
Think about it, after 15 miles of a marathon have passed and you look at your watch. You are 1 minute and 30 seconds behind your pace. Are really going to be able to pick up it 10 second per a mile from there to the finish? Most of the time, I would say no. That is unless you have run so slowly the first half was under your ability.
When I run a race, I set my Garmin to auto track the splits and then forget about it. The next time that I look at it is when I have crossed the finish line.
The thing that I like to tell people is trust in yourself. If you are having a good day, you are going to know it. Knowing the splits isn't going to make you run any faster. And the contrast is just as true if you are have a bad race, the split will more than likely continue any downward spiral that you are on. Thus you are better off not knowing.
That's why I tell people to "just go out and run", and let your body tell you what it can do. By spending less time stressing over the splits, you will most have more energy and motivation to drive yourself harder to the finish. And, listen to what your body is telling you and especially monitor your breathing. Both can provide ton of internal feedback when it comes to modulating your race pace.
Happy Holidays from the Cool Down Runner