Thanks Heinz for this excellent description on the actual workings of the decompression bezel although I doubt it will be of much use for me as I don’t plan to take my watches near any water let alone the depths you are talking about. There is another lesson here and that comes in the form of simple oral history, from the actual experience of the original owner. We often get questions about the type of bezel that should be on a particular reference e.g. Siffet = Tachymeter bezel. These stem from the fact that they appear in the original catalogues with a certain bezel and the general perception is that is how they are meant to be. We know that various bezel options were available and we have just heard that one could buy these inter changeable parts from a good dealer or the distributor at the time the watches were sold. If you had a watch e.g. Autavia 1163GMT but wanted to use if for more than one purpose e.g. GMT time, diving and/or motor racing, the smart buyer/tool watch user would change the bezel as and when required. Heinz is a case in point. So next time we see a Siffert with a MH bezel or Orange Boy with a decompression bezel one thing is for certain – they are correct and the way the original owner wanted it. I remember when I bought my first Siffert with MH bezel there was a Siffert expert who stated categorically that it was incorrect. It happened to come with the original paperwork with the reference noted as 1163MH but that information was not made public at the time.
This is probably not news to the experienced collectors but may be of some use to those who question the configuration of a watch and the accompanying bezel.

Regards
Paul
www.heuerworld.com