Wing Frequency measuring app

This is a useful thread. Checking the wing resonant frequency annually, and after a bad landing, does sound a good idea, although I'm not aware that it is required at annual inspections in the USA, unless the manufacturer has specified it. My glider documentation has the factory measurement (110 per minute) resting on main wheel and tailwheel. On my check out, I was instructed to set the wings vibrating at every daily inspection, but only told to look for crinkles appearing in the wing surface, or unusual squeaking noises. I hadn't heard that the tip phase was good to look at. I'd probably buy an app for $1 if it was for the iPhone, but also I think it would be pretty easy to do accurately with a normal digital watch.