If you have an android phone, you can get the app called MyTracks from Google. I used this when I walked on a regular basis to get a general idea of how fast I was walking and how far. I now use it with my phone tucked away in the little bag under my seat for the same purpose on my bike. It measures change in grade as well and allows you to save your routes. It was free and seems to be pretty reliable. I've also accidentally left it running when I wasn't using it and it didn't seem to adversely affect the battery life of my phone either.