Does anyone have any advise on how to set the above correctly. I had it set to what I thought was my correct stride but on running a half marathon on Sunday it told me I had only run 10.5 miles. However yesterday when I ran my normal 3.2 route (taken from the car) it is telling me that I did a distance of 3.3 which is quite close. How can I set to make sure it is giving me correct distances without having to check again or is this model (given as a present) just not up to scratch??