From Chinese Watch Wiki

Zuanshi (钻石) was a grade 1 watch brand produced by the Shanghai ZuanShi Watch Factory . The name means "diamond", and Diamond-branded watches were manufactured for export to Western countries. The brand's logo was a side-view of a round cut diamond. Zuanshi 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 watches using the Standard movement. This exemption was granted due to the high quality of the SM1A movement used in Zuanshis.

Between 1972 and 1983, Zuanshi watches were awarded the national "No.1 wristwatch" watch a total of ten times.

The Zuanshi brand was also applied to mechanical stopwatches, some of which saw military use, and household alarm clocks.