The large balance wheel, similar to those found in a fine watch, runs in ball bearings. The center arm of the balance wheel iis a wound electromagnet. Electrical contacts connect the battery circuit to the electromagnet in the balance wheel, timed to keep the wheel in motion. A ratchet gear train connects the balance wheel to the hhands on the clock face.

The Eureka clocks were made in Ehgland and Germany from about 1912 and later, all nicely finished and available in a variety of cases, the glass domed model being the most sought after.