While we look at wrist watches as a very commonplace
After the mainspring was invented in the 15th century, wrist watches were invented as it was not possible to make these before the invention of the mainspring. Patek Philippe in 1868 invented a portable watch that was intended to be a lady's bracelet watch. It was thought of as jewellery and was thus 'unmanly,' so males did not wear them.
However, in 1904 Cartier was asked by an aviator friend to make a watch that could be used during flights. He invented the Santos wristwatch which was the first wristwatch made for men, and was designed to be practical in use. These became very popular during World War I as officers could use them easily, unlike a pocket watch which was inconvenient.
Since watches were designed to be practical implements to be used while men were working, it made sense to design them to be worn on the left hand, as most people are right handed, so that it would be easy to both hold a weapon and look at the time at the same time.
Furthermore, since early wristwatches had to be wound, they were worn on the left hand with the winding knob facing outwards so that the person wearing it could easily wind it up using their right hand, and not have to face the inconvenience of having to use the wrong hand to wind it up.
Another reason for wearing wristwatches on the left hand is that the watch does not get damaged easily. Since we use our right hand for most actions, if we wore our watches on the right hand we would inevitably end up banging it into things a lot and thus breaking it sooner.
Finally, it is possible that the arm the watch was made for was based simply on the whim of the first inventors of the wristwatch.
Regardless of the reason, people nowadays wear the watch on whatever hand seems more convenient to them. Professionals such as construction workers, doctors' etc wear watches on left hand, while many other people choose to wear the watch on the right hand. Of course, left-handed people now wear watches on the right hand since it is more convenient for them.
Since, there is now 'right' arm to wear the watch on; they are now made so that they can be worn on either warm. Modern wristwatches do not need to be wound, thus making it possible to wear them on whichever arm is more convenient for the owner of the watch, regardless of what history may have to say on the topic.
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