Shanghai 上海 Watch Factory's most common models in the late 1960s and early 1970s were manufactured with the SS1 movement, an upgrade from the 581/611 movements used previously. The SS1A could be the first model to use the new movement. This one's date code, BC, dates it to March 1967. After a short run with this designation, Shanghai Watch Factory SS1 watches usually had four-digit model numbers beginning with 10, 11, or 15.