The account books of the Tong Taisheng 统泰升 grocery store in Ningjin county of northern China in 1800–1850 constitute the most complete and integrated surviving archive of a family business in premodern China. They contain unusually detailed and high-quality statistics on exchange rates, commodity prices, and so on. Utilized once in the 1950s, the archive had been left largely untouched until our recent, almost accidental rediscovery. This article introduces this unique set of materials and traces the personal history of the original owner and donor. The story of this archive encapsulates the history of modern China and how the preservation and interpretation of evidence and records of Chinese economic statistics were profoundly impacted by the development of political ideology in modern and contemporary China. We briefly discuss the historiographical and epistemological implications of our findings for the current Great Divergence debate.