There were two thin movements. One is Diamond's "B" type 17 jewels movement of 3.75mm thickness, and another is Beijing's standard 17 jewels movement of 3.7mm thickness. The "B" movement has a higher accuracy(+,-25 s/d) than the standard movement and was awarded a silver medal of national quality products.
Shanghai developed a 35 jewels automatic movement based on this "B" movement. This 35 jewels movement is found in many "international" brands watches, and is of very good quality.
The Yan Shan is also a Beijing made watch brand. These watches resemble some of the top brand watches in style. :-D