All around useful.

I really enjoy using this app. It works all over the world for knowing how fast ones train is traveling to the ferry when out in the middle of nowhere between countries.

It is also very useful in being able to guess ones arrival time based on current and previous travel speed. This is especially true if your hydrofoil can maintain top speed due to rough seas. :)

I got this app when I first had access to gps in my iPhone and still use it with my iPhone 6.

the_clangers about Speedometer Speed Box, v5.2.4