hHow inflated (or under-inflated) a football is can affect how the ball moves when kicked. You can throw your antiquated pressure gauge away, though, because there's now an app called BallTune that can calculate a ball's internal pressure simply by listening to it bounce.
Available for both iOS and Android devices, using the app is as simple as pointing it at a soccer ball that's then dropped onto a hard surface. BallTune records a video and then analyzes the sound and frequency of bounces to calculate the ball's PSI, allowing you to then tune adjust it for a specific behavior based on recommendations in the app.
Normally the app will run just two bucks, but because the World Cup is currently on, it's free for a limited time. And eventually its creators plan to release versions for basketballs and volleyballs too. [BallTune]