This app emulates the Telemeter bezel of analog watches, it allows you to determine the distance of an event based on the speed of sound.
For example you can determine the approximate distance to a storm by counting the time between first seeing the lightning and then hearing it.
You can download & install this app to your garmin device here: https://apps.garmin.com/en-US/apps/430a29c3-9d5e-4fb5-a2e2-9dc44f026a0a