The present Bubble Back features a very unusual and rare configuration, with sweep centre and subsidiary seconds displayed at the same time on the dial. Movements with this experimental characteristic are known to have been made by Omega in extremely limited quantities in the mid 1940s, but never commercialized, thus it can be assumed that Rolex watches with these prototype calibers were an attempt to explore this kind of complication. A similar piece featuring sweep centre and subsidiary seconds dial, a big Bubble Back reference 5028, has been recently sold (October 2023) at Monaco Legend Grouop auction for 120,000 euros