Omega ladies watch 17mm diameter

Hello all,

Not long ago I posted a story about an Omega Seamaster chronograph that my grandfather had bought and I bought from my uncle last month.
I had it serviced and showed my uncle the result.

He was so impressed with the outcome that he decided to give me the watch that belonged to my grandmother. This is also an Omega, it has a 17mm diameter and an aftermarket bracelet.

Can anybody identify it? I haven’t opened it because I don’t know how without messing with it. So I don’t know any serial numbers or movement numbers.

Not going to get a lot of information without opening it up.

If I were a betting man, my money would say that contains a cal 661...

http://www.ranfft.de/cgi-bin/bidfun-db.cgi?10&ranfft&&2uswk&Omega_661

but as to the reference : as @efauser said, need to get her opened...

even though that crown is relatively big, still what a pain!

Thanks for all the replies!

How do I open this piece?