From Chinese Watch Wiki

Zhongshan (钟山/中山) was a grade 4 watch brand produced by the Nanjing Watch Factory . The name means "Bell Mountain", and was an earlier name for a mountain peak near Nanjing, which is today known as Zijin Shan or Purple Mountain . Zhongshan watches were noteable for being one of only three watches not powered by the Chinese Standard Movement whose production was allowed to continue after most factories were mandated to produce only the Standard movement. This exemption was granted in order to provide a very low cost alternative to Standard movement watches for the poorest Chinese workers. Zhongshan watches used the SN2 movement, which has a drastically simplified design compared to any other vintage Chinese movement. Despite this focus on cost-saving, Zhongshan watches used stainless steel cases (as opposed to the cheaper chrome-plated brass cases some other brands used). Zhongshan watches are popular with collectors of vintage Chinese movements due to the diverse range of elaborate textured dials which were manufactured.