TheThunderTimer app for iPhone and iPad

Imagine you notice a thunderstorm approaching. This app lets you estimate the distance between you and a thunderbolt. The use is very intuitive:

• When you notice a lightning, tap the button;
• As soon as you hear the thunder, tap again;
• Your distance to the lightning will be displayed, together with the expanded measurement uncertainty following the ± symbol;
• By tapping on this result you may open a map showing your location and the probable region of the lightning stroke.

Metrological background:
The distance is estimated by the elapsed time between lightning and thunder. The main uncertainty contributions are the variability of the acoustic velocity and physiological effects. The average difference in reaction time between visual versus acoustic stimuli are accounted for. The annular uncertainty region shown in the map is additionally increased by the positional accuracy of the observer.