The Circular S Collection is a tribute to the sun which has been providing sustainable energy to our daily lives for a significant amount of time. Circular S for Solar. For the first time in the industry, the recycled steel is re-melted in a solar furnace! The marking "Sun" located in the back of the watch certifies its recycled and melted origin. The carbon footprint of this steel is 165x lower than standard steel certified by an independent expert in environmental performance.