The device consists of two synchronous-oscillation pendulums. The pendulum on the right has a steel magnet at the end. The two pendulums are moved by a clockwork system and are connected to a single counter that records the number of oscillations of each. Below the pendulum on the right there is a coil through which electric current flows. The oscillation period of the right pendulum is greater when a stronger current passes through the coil.

The difference in numbers of oscillations between the pendulums is recorded on the dials of the instrument, from single figures up to tens of thousands of ampere-seconds.
The sheet fixed inside the door shows how to read the quadrants: a section of the upper quadrant corresponds to 0.68 As.

Place and date of construction: Berlin, 18 August 1890.

Acquired in 1903.

Restored in 2017 by Paolo Brenni and Anna Giatti in the Fondazione Scienza e Tecnica laboratory in Florence.

Instrument on display.