Only a little to add to what Mel said. When I run across one of these, I look for a movement number, (usually semi-hidden under the balance) and try to reference it at
http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&0&2uswk. You won't get a complete identification, but you can find some information, usually including the general era.
