Roman numeral dating
The thing is, there's no law specifying that people have to make or not make clocks with Roman numerals.
The best one can do is estimate when doing such a thing began to go out of fashion.
UPDATE 2013-01-12 (or 12/I 2013 ;-) ): After having the (real-life)-feedback of a knowing person: The watch might be from the early 19th century regarding the clockwork mechanics (wooden plates are keeping the gears in place, instead of metal plates as done in newer clockworks).
The following rules apply to subtraction: Only powers of ten (I, X, C, M) can be subtracted.
The smaller letter must be 1/5th (one-fifth) or 1/10th (one-tenth) the larger one.
It did not seem German-like (they usually prefer dots over slashes), but I've found letters from Marc Chagall
id=WXI6K9v PLfk C&pg=PA347 that use Part 1: Assuming dating relating to clocks First of all, there probably still are clocks made with Roman numerals or what not these days.
In this case, a letter with a smaller value precedes one with a larger value and the value of the smaller is subtracted from the larger.