That is a very nice pair Molle. I like mechanical slide rule watches a lot also. Keep them mechanical though as the electric ones will go south someday.

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Even if a steel part for an old watch is no longer available, a watch restorer could make one.

With the advances of semiconductor technology the production lines for the old parts are torn up and thrown away. Even if you had the design information of those old ICs there are no production lines available to make them any more. Of course it is theoretically possible to make them again, but the investment needed is many, many, many orders of magnitude more than you need to make a steel or brass part.

Electronics is throw away technology, even at the low temperatures of watch ICs the doping will wander with time. At some point one of the transistors will stop working and.. there you have it. In 100 years our mechanical watches will all be still working or at least servicable. Maybe you will replace the springs with newer steel, but they will work. The quartz watches all be comfortably filling a waste heap somewhere.