The principal design of gear trains and transmissions is similar to Sørnes' fourth and final clock, arguably the most complicated of its kind. Completed in 1967, clock No. 4 was made in Sørnes' spare time, with his own funding, and using his own self-made tools. The clock was exhibited at the Time Museum in Rockford, Illinois beginning in 1967. In 1999, it was transferred to Chicago Museum of Science and Technology for display, until it was sold to an anonymous bidder at auction in 2002. Its location is currently unknown.