Knowing how you’re doing as you take part in a run or just keeping track of your own set goals a monitor/training device, that’s GPS enabled, can keep track of your pace and distance covered. Watches like the Garmin Forerunner 10 is an example.  Its virtual pacer will alert you if you go above or below your set pace. Which is a great feature if you need to hold back at the beginning of a race because you start off too strong, then have a difficult time of keeping that strong pace at the end.  The same would hold true for cycling computers like the Garmin Edge 810.