Oct 28, 2010 - UK based indie developer Gary Sims has released Thunder Clap HD 1.0 for Apple's revolutionary iPad device. Thunder Clap HD is a great tool for learning all about thunder and lightning. It is a simple to use utility to calculate the distance to a storm based on the time elapsed between the lightning and the thunder. When you see the lightning: hit the 'Lightning' button, then when you hear the thunder: hit the 'Thunder' button. The distance to the storm will be shown.