This is an old fashioned instrument which works actually still very well. Nowadays, we have lots of satellites in the sky telling me my exact speed over the ground in one thousands of a knots accurate. But what does that mean if we have a countercurrent? Exactly, no satellite can tell me my speed through the water. This instruments does what satellites can't. And this patent is almost hundred years old, unchanged. It is nothing more than a simple turning fin on a rope connected to a flywheel and measuring unit. Very accurate and still doing what modern satellites can't do. Telling me my exact speed through the water in order to determine the current rate.
- Nikon D50