You can either do this from the web page on the internet or it will also work if you save it onto your laptop.
Simply type in the distance that you are using (as long as possible - 5-10 m would be ideal). Get the patient walking a few steps before they enter the measured walkway and hit the Start button as they enter it. Count the number of steps and hit Stop (same button so you don't have to look at the computer) when they finish walking the known distance. Sounds tricky but it's really quite easy.
By entering the leg length you can see how close the patient is to normal.
Good luck and let me know if you have any problems!