My friend Kent Mason has developed a substantial collection of old railroad watches, which are highly accurate pocket watches that were required to go through rigorous cleaning and adjusting several times a year.

This c. 1900 beauty by the Illinois Watch Company has a solid metal back that can be unscrewed for access to the innards. I was riveted by its very complex, miniature mechanisms as well as the workmanship.

The second photo below is roughly an inch across. I was unable to read the lettering on the right with the naked eye, and was pleasantly surprised when I saw it in the macro photograph.

Note the number of layers of gears plus the blue spring.