Automatic watch
 

       A wiki link on the subject is at:  http://en.wikipedia.org/wiki/Automatic_watch
 

Poster's notes:

               The key thing to know is that an automatic watch does not need batteries to run. Most people use to have automatic watches (usually very accurate) before battery quartz watches appeared, which do work very well when the battery is good.

               Knowing the correct local time (that you trust) can be a big deal when it comes to things like security patrol and eating schedules.