 One way to identify these functions would be to ask the watch designer, why did you do this the way you did? Failing that, one could consult the written comments by the designer about what each part is supposed to do and why the watch was designed in a particular way rather than in another way. The watch designer's views are highly probative, not because they have some legal power over a watch user, but because of what they know about watch design in general and the choices they made when designing it.