Quite rare, this diamond framed Quadrant. It was for sale at Sterba and he still shows the pictures on his website.
Robert Sterba sold it as being 1890, which is possible. I just found it in the 1892 (French) catalogue, where it is called the Quadrant no. 20.
Look at the details, like Quadrant suspension saddle and the very special bracket! Click picture for a link to Sterba's site.