I've never seen this before, but it looks like a simple tool that won't break or run out of power:

http://en.wikipedia.org/wiki/Pace_count_beads

Another article about it:

http://www.briangreen.net/2010/07/measuring-your-distance-using-strides.html

We learned that in combat training at the School of Infantry. It works well in practice too, not just on paper. One thing, you need to learn to adjust your count for traveling over hills. Picking a landmark in your line of travel and walking directly toward it is a good idea too since you can't stare at your compass 100 percent of the time.