I too have one of these. Mine is from that period of time when the Frey family sold the company - and before they became affiliated with MontBlanc (the early 2000's). Spectacular movement. The original Minerva 13-20 dates from 1923. And these newer versions of it are essentially the same, although with significantly better finishing. It's a nearly 100 year old calibre. It's old school: column wheel, horizontal coupling, etc. Still functions perfectly. I wonder if, in 2023, Montblanc will celebrate the 100 year anniversary of this historic caliber?