Rose P
Fantastic machine! Harris imported machines from Germany made by different manufacturers. The fact that it is made in Stettin means that you can identify it as being made (in all probability) by Stoewer. Have a look at my Serata treadle, made by Stoewer, here at post 116 onwards
http://www.quiltingboard.com/vintage...t130994-3.html
You should clean it up and get it working - you will never regret it. It is far too good just to use as a decoration. The top thread is straightforward for threading, the shuttle is loaded the same way as any other long bobbin machine and the only tricky bit will be the bobbin winder. What if I do you a video on Youtube? I've been dying for an excuse to use my Serata for a video.
I think the serial number is from about 1916. I say this because I have two Seratas both from 1913 and the serial numbers both start with 13. You can always email the Stoewer Museum in Germany and there is a nice man there called Manfried who will tell you for sure whether it is a Stoewer, and if so, date it. If it is 1916 then that is about as late as you get for a German import to this country in the First World War.