Wrist watch Shabbos

 Igros Moshe (OC I #111) Question Can a wristwatch on Shabbos? Answer  It is obvious that a pocket watch is prohibited.  Even those that are worn attached to clothing are  not regarded as jewlry or being worn. However a wristwatch that is actually on the wrist is like a garment. A proof that this is permitted is that a signet ring is permitted even though its use is prohibitd on Shabbos. Furthermore even if the signet ring is damaged and can’t be used for signatures it is permitted to br worn since it is worn on the body even though it is not viewed as a piece of jewlry. Its entire purpose is as a useful device. In a similar manner a scarf which is worn around the neck to clean the mouth and eyes (according to Rashi) and that is its basic reasoson for being worn. Thus it is merely the fact that it is useful that it is permitted to be worn and it is not considered carrying.  Thus a watch worn on the wrist should be  permitted even though it is only worn for the service it provides. While because of this reason there is no reason to protest against those who wear a wristwatch, it is appropriate for every ben Torah and G-d fearing man not to wear a wristwatch on Shabbos. This is to prevent others from thinking that all clocks (such as a pocket watch) are permitted even if attatched to the clothing. Because there is widespread ignorance and this is what I tell my students.