What is this?

by Kim
((Michigan, USA))

What is this?

Does anyone know what the heck this is? There is no make/model anywhere on the watch. It was my nanny's, dated at early 1900's. It was purchased in Rotterdam, Netherlands.

The only words I can make out are in German for "fast" and "slow". Have taken to a jeweler and antique dealer, both said it's a rare piece but have no idea of what it is. It has a key and does work.

If you have any ideas, reply to: seraph@prodigy.net