From the " Dirty Dozen " watches which are Eterna, Omega, JLC, IWC, Longines, Cyma, Buren, Lemania, Timor, Record, Vertex, the Grana is the rarest one, with much less than 5000 watches made. Some say around 1000, compared to the 25, 000 pieces made by Ome...
This image I have copied from Bonhams's sale catalogue looks the same. Estimated values £15,000 to £20,000. Rare indeed! Hope I haven't caused any wrongdoing by advertising this. Clive ...