We MAY wear a mechanical, automatic watch on Shabbos. We may use a tool – normally designed for a labor that is prohibited on Shabbos – to perform a different, permitted labor. Objection is raised to this principle from the example of a mortar and pestle, which are basically off limits on Shabbos, but turn out to be in the category of objects set aside from Shabbos due to fear of financial loss. This includes the special tools of a craftsman that may be damaged if used for other labors, and thus no one would contemplate using them on Shabbos. A different question is whether a muktzeh (set-aside) object may be moved ion Shabbos because we need its place, as when someone mistakenly leaves their cell phone on the dinner table before Shabbos. We move it in an atypical manner to show we know it’s muktzeh. Muktzeh law is generally lenient in cases of doubt because it is based on rabbinic decree, whereas doubt re Torah law is handled stringently.