The idea is great and the measurement process (at least the only one I can use, 1s) work well. The problem is that, at least on my iphone 3GS the interface is not working correctly. The screen appears to be cut in half and I cannot change the target speed. Once it reads and you want to set the pick values by zooming in, it will not stay when you zoom out, and it is difficult to do it on small scale. Also it's a bit of a bummer that you cannot organize your camera in the list, after inputing them, or delete a reading (you have to replace it with a new one). Upgrade, my friend? I would like to keep on using it, as I have several old cameras.