Ekman current meter

The ball falls into one of thirty-six compartments in the bottom of the compass box that indicate direction in increments of 10 degrees.

This is a simple and reliable instrument whose main disadvantage is that is must be hauled up to be read and reset after each measurement.

Ekman solved this problem by designed a repeating current meter which could take up to forty-seven measurements before needing to be hauled up and reset.

This device used a more complicated system of dropping small numbered metal balls at regular intervals to record the separate measurements.

Harald U. Sverdrup, Martin W. Johnson, and Richard H. Fleming, The Oceans: Their Physics, Chemistry, and General Biology, Prentice-Hall, Inc., 1942